<PAGE>

                                                                   Exhibit 10.28

                            ASSIGNMENT OF RIGHTS IN
                           STOCK PURCHASE AGREEMENT

WHEREAS:

a.   On January 31, 2000, William McKay entered into a Stock Purchase Agreement
     (the "Agreement") with Smith Acquisition Company, Inc., d/b/a Southwest
     Products Company, Inc. (the "Company"), Sunbase Asia, Inc. and Samuel T.
     Mok, Trustee, to purchase all of the outstanding stock of the Company from
     Sunbase Asia, Inc. and Samuel T. Mok, Trustee.

b.   The Agreement does not permit the assignment of a party's rights under the
     Agreement without the written consent of the other parties.

c.   As previously disclosed to the Trustee, William McKay wishes to purchase
     the Company stock with two other current management employees of the
     Company, so that their combined ownership of the Company will be William
     McKay - 70%, Frank P. Brothers - 15% and Gary S. Horany - 15%.

d.   The lender who will be financing the purchase has requested that its loan
     be made directly to the Company rather than the individual purchasers.

e.   In order to structure the purchase with a loan to the Company, William
     McKay, Frank P. Brothers and Gary S. Horany plan to create a new
     corporation which will actually purchase the stock of the Company and
     simultaneously merge with the Company, leaving the Company as the surviving
     corporation. That would place the loan with the Company as requested by the
     lender, and the Company would be owned 70% by William McKay, 15% by Frank
     P. Brothers and 15% by Gary S. Horany.

                                       1
<PAGE>

     f.   Accordingly, William McKay wishes to assign his right to purchase all
          of the stock of the Company to the new corporation to be formed under
          the name "McKay, Brothers & Horany Acquisition Corp.," the shares of
          which will be owned 70% by William McKay, 15% by Frank P. Brothers and
          15% by Gary S. Horany.

     g.   The Company, Sunbase Asia, Inc. and Samuel T. Mok, Trustee, wish to
          consent to that assignment.

     ACCORDINGLY:

     William McKay hereby assigns to McKay, Brothers & Horany Acquisition
Corp., a corporation owned 70% by William McKay, 15% by Frank P. Brothers and
15% by Gary S. Horany, all of his right, title and interest in and to the
Agreement, including all of his duties, obligations and responsibilities
thereunder. William McKay acknowledges and agrees that this assignment to McKay,
Brothers & Horany Acquisition Corp. will not relieve him personally of any of
the duties, obligations and responsibilities he has under the Agreement or any
other agreement or guaranty executed in connection therewith.

Dated: March 24, 2000                    /s/ William McKay
                                         -----------------------------
                                         William McKay

                           ACCEPTANCE OF ASSIGNMENT

     On behalf of McKay, Brothers & Horany Acquisition Corp., we hereby accept
this assignment and agree to be bound by all of the duties, obligations and
responsibilities of the purchaser under the Agreement.


Dated: March 24, 2000                   /s/ William McKay
                                        ------------------------------
                                        William McKay

                                       2
<PAGE>

Dated March 24, 2000                    /s/ Frank P. Brothers
                                        ______________________________
                                        Frank P. Brothers

Dated March 24, 2000                /s/ Gary S. Horany
                                        ______________________________
                                        Gary S. Horany

                             CONSENT TO ASSIGNMENT

     We hereby consent to the above assignment.

                                          Smith Acquisition Company, Inc.
                                          d/b/a Southwest Products Company, Inc.


Dated: March 24, 2000                     /s/ Samuel T. Mok
                                          ---------------------------------
                                          Samuel T. Mok, Chairman


                                          Sunbase Asia, Inc.

Dated: March 27, 2000                     /s/ Li Yuen Fai (Roger)
                                          ---------------------------------
                                          Li Yuen Fai (Roger), Chief Fin'l
                                          Officer

Dated: March 24, 2000                     /s/ Samuel T. Mok
                                          ---------------------------------
                                          Samuel T. Mok, Trustee

                                       3