Appreciate all the information thus far, this certainly gives me a good base to go off of. A dial intercom seems interesting, but requires tracking down additional hardware. Assuming I can find a KSU, I'll probably start with the manual intercom first.
Arthur: I'm interested in seeing that document. A modification like that would be pretty easy for me to do.
Ed: I imagine the way around that is to manually release the call on the phone in question.
Two other things that came to mind:
(1)From the pictures I've seen, it looks like the KSU power supplies use non-standard fuses for protection. Has anyone ever modified those to use standard fuses and holders, like ACG fuses? I can't imagine it would be that difficult to implement.
(2) Given the age of these units, has anyone run into issues with the electrolytic caps? I imagine a number of the power units would need to be re-capped. Not hard to do, assuming the power unit can be opened.
