Hap- I decapped JR55 and it is an SM510; the die looks just like Top Gun's. SM510 has 44 banks of ROM instead of 64, so if Boxing also uses it, there would be duplicate banks in my ROM dump, and it's possible (although it seems unlikely) that they only needed 31 banks for the code.

I might need to tweak the timing; using the same rig on Cement Factory, I'm not getting the same bytes in bank 55 as I get straight out of reset.

There are no part numbers on the chips, and SM510 and SM511 have almost identical pinouts. I guess I need to come up with a set of instructions that I can send the chips that will distinguish between them.