Reverse engineering circuitry in a Spacelab computer from 1980

Spacelab was a reusable laboratory that could be carried in the cargo bay of the Space Shuttle, providing lab space for astronauts
and experiments.
Spacelab was controlled by a French-built minicomputer, called the Mitra 125 MS.
Unlike modern computers, this computer didn't contain a microprocessor chip.
Instead, its 16-bit processor was constructed from several boards of chips.
In this article, I reverse-engineer one of the processor boards, shown below, part of the computer's Arithmetic/Logic ...