<PAGE>   1
                                                                  EXHIBIT 10.1.3


                     [BENCHMARK COMMUNICATIONS LETTERHEAD]




                                January 31, 1997



Benchmark Acquisition, Inc.
BCR Holding, Inc.
Capstar Broadcasting Partners, Inc.
c/o Hicks, Muse, Furst & Tate Incorporated
1325 Avenue of the Americas, 25th Floor
New York, NY 10019
Attn:  Peter Brodsky


   Re: Agreement and Plan of Merger by and among Benchmark Communications
       Radio Limited Partnership, Benchmark Acquisition, Inc., Benchmark Radio
       Acquisition Fund I Limited Partnership,  Benchmark Radio Acquisition
       Fund IV Limited Partnership,  Benchmark Radio Acquisition Fund VII
       Limited Partnership,  Benchmark Radio Acquisition Fund VIII Limited
       Partnership, Joseph L. Mathias, Bruce R. Spector, Capstar Broadcasting
       Partners, Inc. and BCR Holding, Inc. dated as of December 9, 1996 (the
       "Merger Agreement")

       Credit Agreement (Greenville) dated as of December 9, 1996 between BCR
       Holding, Inc. and Benchmark Radio Acquisition Fund VII Limited
       Partnership as Borrower (the "Greenville Credit Agreement")

       Credit Agreement (Statesville) dated as of December 9, 1996 between BCR
       Holding, Inc. and Benchmark Radio Acquisition Fund IX Limited 
       Partnership as Borrower (the "Statesville Credit Agreement")

       Credit Agreement (Jackson) dated as of December 9, 1996 between BCR
       Holding, Inc. and Benchmark Radio Acquisition Fund X Limited Partnership
       as Borrower (the "Jackson Credit Agreement")

       Credit Agreement (Montgomery) dated as of December 9, 1996
       between BCR Holding, Inc. and Benchmark Radio Acquisition
       Fund XI Limited Partnership as Borrower (the "Montgomery
       Credit Agreement" and, together with the Greenville Credit
       Agreement, the Statesville Credit Agreement, and the Jackson
       Credit Agreement, the "Credit Agreements")




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Benchmark Acquisition, Inc.
BCR Holding, Inc.
Capstar Broadcasting Partners, Inc.
January 31, 1997
Page 2


          Side Letter Regarding Capital Expenditure Loans entered into by and
          between Benchmark Acquisition, Inc. and Benchmark Communications
          Radio Limited Partnership as of December 9, 1996 (the "Capital 
          Expenditure Side Letter")


Ladies and Gentlemen:

          This letter, when signed by each of us and the other parties to the
Merger Agreement and the Credit Agreements, will memorialize the parties'
agreement with respect to the matters set forth herein. Capitalized terms in
paragraphs (1) through (5) and in paragraph (9) below not defined herein shall
have the meanings assigned to such terms in the Merger Agreement. Capitalized
terms in paragraphs (6) through (8) below not defined herein shall have the
meanings assigned to such terms in the Credit Agreements.

          The parties hereto agree as follows:

       1. Section 1.6(f) of the Merger Agreement is replaced in its entirety
with the following clause (f):

          (f) BCF Calculation.

              (1) Benchmark will use its commercially reasonable efforts to
       close the books of Benchmark, Fund I, Fund IV, Fund VII and Fund VIII by
       February 3, 1997 in a manner that will enable Coopers & Lybrand to
       conduct an audit (the "Coopers Audit") of Benchmark and each of Fund I,
       Fund IV, Fund VII and Fund VIII on a consolidated basis for the fiscal
       year ended December 31, 1996. Mergeco shall use commercially reasonably
       efforts to cause Coopers & Lybrand to perform the Coopers Audit in the
       manner described in this Section 1.6(f)(1) and to take the actions
       described in this Section 1.6(f)(1), and Benchmark will permit Coopers &
       Lybrand to perform the Coopers Audit subject to the following
       conditions:

                  (A) Benchmark shall be promptly reimbursed by Mergeco for
          audit fees not to exceed $20,000 charged by Arthur Andersen LLP in
          connection with the audit of Benchmark, Fund I, Fund IV, Fund VII and
          Fund VIII for the 1996 fiscal year that was commenced (but not
          completed) by Arthur Andersen LLP;

                  (B) Except to the extent set forth in Section 1.6(f)(2), no
          audit other than the Coopers Audit shall be conducted for purposes of
          preparing the BCF Calculation;



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Benchmark Acquisition, Inc.
BCR Holding, Inc.
Capstar Broadcasting Partners, Inc.
January 31, 1997
Page 3

                  (C) Coopers & Lybrand shall promptly make available to
          Benchmark any proposed audit adjustments in connection with the
          Coopers Audit, and any such adjustments must be approved by
          Benchmark;

                  (D) Coopers & Lybrand shall be responsible for all word
          processing in connection with the Coopers Audit, and the financial
          statements contained in the Coopers Audit shall be in substantially
          the same format as the financial statements contained in the Coopers
          & Lybrand audit report relating to Benchmark, Fund I, Fund IV, Fund
          VII and Fund VIII for the nine months ended September 30, 1996;

                  (E) Coopers & Lybrand will conduct its field work at the
          Benchmark's offices between February 3, 1997 and February 10, 1997
          and will have all field work completed no later than February 15,
          1997;

                  (F) Confirmations for accounts receivable and cash will be
          rolled forward from September 30, 1996 and will not be required for
          the Coopers Audit unless material variances, in the opinion of
          Coopers & Lybrand, exist to warrant such testing;

                  (G) The field work of Coopers & Lybrand will consist of the
          items outlined in the client assistance schedule provided to
          Benchmark by Coopers & Lybrand, and such schedule will be modified to
          reflect that Item 3F should read "significant accounts greater than
          120 days;"

                  (H) The fixed asset appraisals for stations acquired by
          Benchmark or any Fund during 1996 will be set up in summary form and
          not entered individually into the fixed asset system;

                  (I) Coopers & Lybrand shall (i) schedule in the notes to the
          report of Coopers & Lybrand relating to the Coopers Audit (the
          "Coopers Audit Report") the 1996 income for each of Fund I, Fund IV,
          Fund VII and Fund VIII (the format for this schedule will be the same
          as the one provided by Benchmark to Coopers & Lybrand in connection
          with the September 30, 1996 audit by Coopers & Lybrand and shall
          include each Fund's income statement with the appropriate elimination
          entry in the format that such items appeared in the workpapers of
          Coopers & Lybrand relating to the September 1996 audit), (ii) include
          in its work papers relating to the Coopers Audit and the Coopers
          Audit Report (the "Coopers Work Papers") the 1996 income for each
          individual radio station operated by Fund I, Fund IV, Fund VII and
          Fund VIII and (iii) upon receipt of customary releases, make
          available no later than February 22, 1997 to Benchmark and Arthur
          Andersen LLP the Coopers Audit Report and the Coopers Work Papers;
          and


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Benchmark Acquisition, Inc.
BCR Holding, Inc.
Capstar Broadcasting Partners, Inc.
January 31, 1997
Page 4

                  (J) All inquiries of Coopers & Lybrand to Benchmark regarding
          the Coopers Audit shall be made prior to February 15, 1997.

              (2) Benchmark shall use its commercially reasonable efforts to
     cause Arthur Andersen LLP to, pursuant to certain agreed upon procedures
     (the "Agreed Upon Audit Procedures"), perform a limited audit of the
     applicable balance sheets and income statements in order to calculate the
     Statesville Broadcast Cash Flow, the Jackson Broadcast Cash Flow and the
     KRMD-AM/FM Broadcast Cash Flow (which shall constitute a component of the
     Fund IV Broadcast Cash Flow). Arthur Andersen will qualify its report
     relating to such audit to disclose that a statement of cash flow and
     retained earnings and full footnote disclosure has been omitted from such
     report.

              (3) No later than April 30, 1997, Benchmark shall deliver to
     Mergeco a certificate executed by the General Partners of Benchmark, dated
     the date of its delivery, setting forth the calculation of Fund I
     Broadcast Cash Flow, Fund IV Broadcast Cash Flow, Fund VIII Broadcast Cash
     Flow, Statesville Broadcast Cash Flow, Jackson Broadcast Cash Flow and
     Montgomery Broadcast Cash Flow on which the Fund I BCF Consideration, the
     Fund IV BCF Consideration, the Fund VIII BCF Consideration and the
     Benchmark Consideration will be based (the "BCF Calculation"). The
     certificate will state that the BCF Calculation has been certified by
     Arthur Andersen LLP and is based on (i) the terms of this agreement, (ii)
     the Coopers Audit Report and the Coopers Work Papers (with respect to the
     Fund I Broadcast Cash Flow, the Fund IV Broadcast Cash Flow and the Fund
     VIII Broadcast Cash Flow) and (iii) the Agreed Upon Audit Procedures (with
     respect to the Statesville Broadcast Cash Flow, the Jackson Broadcast Cash
     Flow and the KRMD-AM/FM Broadcast Cash Flow). The procedures described in
     Section 1.6(f)(2) relating to the Agreed Upon Audit Procedures shall be
     agreed upon by Mergeco and Benchmark in consultation with Arthur Andersen
     and Coopers & Lybrand no later than February 15, 1997. Prior to delivery
     of the certificate setting forth the BCF Calculation, Benchmark shall
     request Arthur Andersen LLP to consult with Coopers & Lybrand regarding
     the preparation of the BCF Calculation and to provide Coopers & Lybrand
     with applicable documentation setting forth the basis upon which Arthur
     Andersen LLP calculated the Statesville Broadcast Cash Flow, the Jackson
     Broadcast Cash Flow and the KRMD-AM/FM Broadcast Cash Flow.

     2.       The following sentence is inserted at the end of Section 1.6(i)
of the Merger Agreement:

              The parties agree that neither Mergeco nor Coopers & Lybrand may
     dispute a component of the BCF Calculation to the extent the disputed
     component was derived from the Coopers Audit, the Coopers Audit Report
     (including the notes thereto) or the Coopers Work Papers and, in the event
     any such dispute is raised, the Referee shall resolve such dispute in 
     favor of Benchmark; provided, however, that 


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Benchmark Acquisition, Inc.
BCR Holding, Inc.
Capstar Broadcasting Partners, Inc.
January 31, 1997
Page 5

         this shall not limit the right of Coopers & Lybrand to dispute the 
         methods pursuant to which numbers contained in the Coopers Audit, the 
         Coopers Audit Report (including the notes thereto) or the Coopers Work
         Papers are applied to calculate any disputed components of the BCF 
         Calculation.

         3.       Article IV of the Merger Agreement is amended by inserting
the following Section 4.14:

                  4.14 New Shreveport Station. Benchmark agrees to consult with
         Mergeco with respect to the incurrence of additional Shreveport
         Expenses; provided that such consultation shall not require Benchmark
         not to perform its obligations under the Shreveport Master Agreement
         or other agreements relating thereto. Mergeco confirms that
         Benchmarks' agreement to so consult shall not change the parties'
         obligation to treat all Shreveport Expenses (including those incurred
         to date) as a portion of the Fund IV Consideration regardless of
         whether the Initial Closing (as defined in the Shreveport Master
         Agreement) occurs.

         4.       The following definition is added to Article XI of the Merger
Agreement:

         "KRMD-AM/FM Broadcast Cash Flow" means the aggregate revenues of
         KRMD-AM/FM during 1996 minus the aggregate operating expenses of
         KRMD-AM/FM during 1996 (regardless of whether such stations were owned
         by Benchmark or its subsidiaries, or any third party, during such time
         period), determined in accordance with GAAP, consistently applied,
         excluding any expenses for (i) depreciation, (ii) amortization, (iii)
         interest, (iv) income taxes, (v) management fees and expenses payable
         to Benchmark or AmCom General Corporation and its affiliates, (vi)
         legal fees and expenses incurred in connection with the sale of
         KRMD-AM/FM and the reorganization of AmCom General Corporation and its
         affiliates and (vii) Shreveport Expenses. In addition, in calculating
         KRMD-AM/FM Broadcast Cash Flow, extraordinary gains and losses
         (determined in accordance with GAAP), gains and losses on sales of
         fixed assets and revenues and expenses under trade and barter
         agreements shall be excluded. In addition, the KRMD-AM/FM Broadcast
         Cash Flow shall be increased by approximately $68,700 to reflect that
         KRMD-AM/FM will receive rental income from tenants at the stations'
         studio building at 3109 Alexander Boulevard in Shreveport, Louisiana,
         will no longer incur studio/office rental expense at such site and will
         no longer incur billboard rental expenses at the station's AM
         transmitter site.

         5. Clause (b) of Section 4.2 of the Merger Agreement is amended by
inserting the words "; provided, however that Benchmark shall not be required
to deliver any of the items referenced in this sentence for the months of
January 1997, February 1997 and March 1997 until April 30, 1997" at the end of
the first sentence of such clause.


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Benchmark Acquisition, Inc.
BCR Holding, Inc.
Capstar Broadcasting Partners, Inc.
January 31, 1997
Page 6


         6. Clause (a) of Section 5.01 of each Credit Agreement is amended by
replacing the words "as soon as available, but in any event within 90 days
after the end of each calendar year" with the words "beginning with the
calendar year ended December 31, 1997, as soon as available, but in any event
within 120 days after the end of each calendar year."

         7. The following proviso is inserted at the end of clause (b) of 
Section 5.01 of each Credit Agreement:

         ; provided, however, that the Borrower shall not be required to
         deliver the unaudited consolidated balance sheets of the Borrower and
         its Subsidiaries and the related unaudited consolidated statements of
         income and of cash flows for the months of January 1997, February 1997
         and March 1997 until April 30, 1997.

         8. Under the Capital Expenditure Side Letter, the date by which the
parties agree to negotiate in good faith the documentation of the Capital
Expenditure Loans (as defined therein) is hereby extended from thirty days
after the date of the Capital Expenditure Side Letter to February 28, 1997.

         9. The parties hereto agree to cooperate in good faith to enable
Coopers & Lybrand to complete the Coopers Audit Report, the Coopers Audit and
the Coopers Work Papers within the time periods specified in paragraph 1 of
this Letter Agreement. The parties recognize, however, that Coopers & Lybrand
(i) are independent public accountants to Mergeco, (ii) are not a party to this
Letter Agreement and (iii) may, in their professional discretion, determine
that they are unable to complete or deliver the Coopers Audit Report, the
Coopers Audit and/or the Coopers Work Papers under the conditions and/or within
the time period specified in paragraph 1 of this Letter Agreement. In the event
the Coopers Audit Report, the Coopers Audit and/or the Coopers Work Papers are
not completed and delivered in the manner and within the time periods specified
in paragraph 1 of this Letter Agreement (regardless of whether Mergeco has used
its commercially reasonable efforts to effect such completion and delivery),
the parties agree that paragraphs 1, 2, and 4 of this Letter Agreement will
terminate and that the original provisions contained in the Merger Agreement to
which such paragraphs relate will remain in full force and effect.




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Benchmark Acquisition, Inc.
BCR Holding, Inc.
Capstar Broadcasting Partners, Inc.
January 31, 1997
Page 7


        Please countersign this letter below to indicate your agreement with
respect to the matters set forth herein.


                                              BENCHMARK COMMUNICATIONS RADIO
                                              LIMITED PARTNERSHIP


                                              /s/ BRUCE R. SPECTOR
                                              ---------------------------------
                                              BY:  Bruce R. Spector
                                              Its:  General Partner

Agreed to and Accepted,

BENCHMARK ACQUISITION, INC.


/s/ PETER S. BRODSKY
---------------------------------
BY:  Peter S. Brodsky
Its:


BCR HOLDING, INC.


/s/ PETER S. BRODSKY
---------------------------------
By:  Peter S. Brodsky
Its:


CAPSTAR BROADCASTING PARTNERS, INC.


/s/ PETER S. BRODSKY
--------------------------------
By:  Peter S. Brodsky
Its:




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Benchmark Acquisition, Inc.
BCR Holding, Inc.
Capstar Broadcasting Partners, Inc.
January 31, 1997
Page 8


        The undersigned parties hereby agree to the terms of this letter
agreement, as of the date first written above.


                                          BENCHMARK RADIO ACQUISITION FUND I    
                                          LIMITED PARTNERSHIP                   
                                                                                
                                                                                
                                          /s/ BRUCE R. SPECTOR                  
                                          --------------------------------------
                                          By:   Bruce R. Spector                
                                          Its:  General Partner                 
                                                                                
                                                                                
                                          BENCHMARK RADIO ACQUISITION FUND IV   
                                          LIMITED PARTNERSHIP                   
                                                                                
                                                                                
                                          /s/ BRUCE R. SPECTOR                  
                                          --------------------------------------
                                          By:   Bruce R. Spector                
                                          Its:  General Partner                 
                                                                                
                                                                                
                                          BENCHMARK RADIO ACQUISITION FUND VII  
                                          LIMITED PARTNERSHIP                   
                                                                                
                                                                                
                                          /s/ BRUCE R. SPECTOR                 
                                          --------------------------------------
                                          By:   Bruce R. Spector                
                                          Its:  General Partner                 
                                                                                
                                                                                
                                          BENCHMARK RADIO ACQUISITION FUND VIII 
                                          LIMITED PARTNERSHIP                   
                                                                                
                                                                                
                                          /s/ BRUCE R. SPECTOR                 
                                          --------------------------------------
                                          By:   Bruce R. Spector                
                                          Its:  General Partner                 
                                                                                

                                                

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Benchmark Acquisition, Inc.               
BCR Holding, Inc.
Capstar Broadcasting Partners, Inc.
January 31, 1997
Page 9

                                        BENCHMARK RADIO ACQUISITION FUND IX    
                                        LIMITED PARTNERSHIP                    
                                                                               
                                                                               
                                        /s/ BRUCE R. SPECTOR                 
                                        -------------------------------------- 
                                        By:   Bruce R. Spector                 
                                        Its:  General Partner                  
                                                                               
                                                                               
                                        BENCHMARK RADIO ACQUISITION FUND X     
                                        LIMITED PARTNERSHIP                    
                                                                               
                                                                               
                                        /s/ BRUCE R. SPECTOR                  
                                        -------------------------------------- 
                                        By:   Bruce R. Spector                 
                                        Its:  General Partner                  
                                                                               
                                                                               
                                        BENCHMARK RADIO ACQUISITION FUND XI    
                                        LIMITED PARTNERSHIP                    
                                                                               
                                                                               
                                        /s/ BRUCE R. SPECTOR                 
                                        -------------------------------------- 
                                        By:   Bruce R. Spector                 
                                        Its:  General Partner                  
                                                                               
                                                                               
                                        /s/ BRUCE R. SPECTOR                   
                                        -------------------------------------- 
                                        Bruce R. Spector                   
                                                                               
                                                                               
                                        /s/ JOSEPH L. MATHIAS, IV               
                                        -------------------------------------- 
                                        Joseph L. Mathias, IV               
                                                                               
                                                                               
                                        

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Benchmark Acquisition, Inc.
BCR Holding, Inc.
Capstar Broadcasting Partners, Inc.
January 31, 1997
Page 10



                                         HOME RUN RADIO LIMITED PARTNERSHIP    
                                                                               
                                         By:   HR Radio Corporation            
                                         Its:  General Partner                 
                                                                               
                                                                               
                                         /s/ BRUCE R. SPECTOR               
                                         --------------------------------------
                                         By:   Bruce R. Spector                
                                         Its:  President                       
                                                                               
                                                                               
                                         GRAND SLAM RADIO LIMITED PARTNERSHIP  
                                                                               
                                                                               
                                         /s/ MICHAEL MATHIAS                 
                                         --------------------------------------
                                         By:   Michael Mathias                 
                                         Its:  General Partner