Printers from military surplus with absolutely no documentation and an obscure interface connector... sounds like a good hacking project.
There's a lot of traces under the chips too.
I'm thinking that if I don't succeed in getting it working. I might strip the board right down, so that you can have an image of the front of the board without having to trash one for yourself.
The "big chip"... Possibly a custom chip just for this device. I've not found any details as yet.
The "smaller chips"... Plenty more details on these:
INTERSIL ICL7642ECPD - S8936 - Dual/Quad, Low Power CMOS Operational Amplifiers
MAXIM MAX232CPE - RS-232 --> TTL converter https://en.wikipedia.org/wiki/MAX232
74HC14N - Hex Schmitt-Trigger Inverters
74HC02N - Quad 2-input Positive-NOR gates
LA-180D 46 062028
That Maxim chip looks like a good place to tap in a serial port at either RS232 or TTL voltage.