Just checked again, and it looks like the bad ROMs are 342-0220-A and 342-0221-A. The working ROMs are 342-0220-B and 342-0220-B.
H3NRY, thanks for the information about the 27C256's. Jumpering pin 1 to 28 seems like it wouldn't be too difficult.
With two different sets of ROMs, I guess I can't pinpoint the bad chip by replacing the low or high rom individually. But I do have a ROM reader circuit that I used for some Apple II+ ROMs around somewhere, I might be able to resurrect that to read off the contents of the chips and see which one is bad.
H3NRY, thanks for the information about the 27C256's. Jumpering pin 1 to 28 seems like it wouldn't be too difficult.
With two different sets of ROMs, I guess I can't pinpoint the bad chip by replacing the low or high rom individually. But I do have a ROM reader circuit that I used for some Apple II+ ROMs around somewhere, I might be able to resurrect that to read off the contents of the chips and see which one is bad.