Keith
The board looked a little sparse. Then I noticed it doesn't have the usual 6850 UART or the 6840 counter timer. I guess those functions are done by the 6522 chip, though perhaps not as well.
The glue logic is one DMPAL16R4 chip and three N82S153 PROM chips. The latter should be trivial to reverse engineer. Apart from the fact they are soldered to the board
I look forward to disassembling the ROM to see which addresses it is accessing, and the way it is using the 6522 as a UART.
Bentendo64
Gee Bartlett
Colin Maykish