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 ( https://hackaday.io/project/168472-hacking-a-cossor-raytheon-husky-printer/log/183787-identified-the-main-chip-still-no-datasheet-though )

That Maxim chip looks like a good place to tap in a serial port at either RS232 or TTL voltage.