One minor correction, I was reading the JEDEC standard for 512K x 8 single-supply EEPROM and I should have been reading the JEDEC standard for 512K x 8 EPROM. On the actual PLCC chips, pin 1 is VPP (so supplying 5V probably means don't go into programming mode) and pin 31 is indeed A18. So that removes the two concerns I had about the wiring of the PLCC chips themselves.