Hi!
Since you mentioned that the system is using an EPROM, what type is it? Maybe there's a way to emulate it
If it's a parallel eeprom/nor flash, the memsim2 might be worth a look. Beware though that if the mainboard has +12V connected to the programming voltage pin or another unused pin of the socket, that'll fry the memsim2, so build a small adapter that doesn't connect those two pins, but connects the rest. There's also an open source tool to push the firmware image to the emulator; haven't tried the vendor tool.
Regards Felix