By the way, the part number on this SNAP extension cartridge is RL-
P9001 if that helps.
Also, I just noticed that there is another circuit board mounted
underneath the one with the EPROMs that contains lots of other chips:
M74LS22P, M74LS08P x 2, HD14002BP, M74LS00P, M74LS138P, M74LS02P,
MC14013B, MC14011B.
I guess this is more than just an EPROM expansion board.