Other changes
There are three NIUs (NIUs are the cards inside of the two slot mounting cases, not the case themselves) in the first picture, not two. The single card in the left case looks to be either a HDSL or HDSL4 NIU. The left card in the left case is a HDSL2 NIU. More accurately, those are HTU-R (or H2TU-R or H4TU-R) cards, that terminates HDSL data and outputs a DS1 signal, functionally similar to older T1 NIU, but are not compatible with a T1 system.
Explanatory information on variants (T1C (two concantenated T1s), etc.
From a service provider to a customer, it would look something like
[DSX-1}{ORB]3kft[RPTR]6kt[RPTR]...[NIU][CSU][DSU][CPE]

showing the spacing between the office repeater in the office repeater bay (ORB) and the first line repeater as 3000 
feet (3Kft) and spacing between subsequent repeaters as 6Kft.
Emphasis (at least orginally) on T1 as being a span system.
Designed as a short haul interoffice transport for use inside the telephone companies, and as part of T Carrier System linking two D1 channel banks:
[D1 bank][DSX-1]X[DSX-1][ORB][RPTR]....[RPTR][ORB]DSX-1]X[DSX-1][D1 bank]
Links to other (analog) carrier systems, showing T1 development in context.