My father installed those systems in the 70's. He even custom wired them to utilize the Northern Telecom SM-1's and Logic 10's.
The 1A2 KSU was made by ITT. Each multibutton telephone requires a 25 pair connection to the KSU (If it is a 10-button ITT Classic)=20
I might be able to find the old ITT manuals which have the punch down configurations for all the features, including intercom.
The Ksu requires the old relay line cards.