If you're in to period dumb terminals see if you can figure out what the hell this thing I uploaded to Wikipedia used to connect to: https://upload.wikimedia.org/wikipedia/commons/9/95/4800-52-...

Not that I would be able to help, but do you have a picture of the back and the connectors?

Nope. It was donated to ACMS https://www.acms.org.au/

Anything written on the PCB? Switch type/brand?

A lot of equipment used keyboards that are not necessarily dumb terminals.

Sorry, never opened it and I don't recall opening it (it was all I could do to photograph my hardware, upload to Wikipedia and get it to a potentially good home in lieu of losing it to the rubbish). However, I just noticed it has an interesting character: according to https://en.wikipedia.org/wiki/Tilde#Similar_characters it is the REVERSED TILDE. Maybe that is a clue. Not being maths trained, I also stumbled on ∺ (geometric proportion) which seems interesting and appealed to me as a potentially n-dimensional 差不多 :)