I can dump the 1650 right now, btw. I got a Tandy Cosmic Fire Away 3000 today (aka twinvader III, which it says right on the PCB)
This has the exact same chip set that the Tsukada games have, a TMS1024 and an MP1604. both are 28 pinners. It also appears to have the same resistor networks too.
I found TMS1024's on ebay so we might want to get one of those decapped if we can't find a data sheet. I didn't have much luck when I poked around google. Apparently the '1024 is an "IO expander" which would make sense for a TMS11xx which has really crappy IO out of the box.
The 1024 should be fairly to RE too I guess since it'd be trivial to hook it up to my logic analyzer to probe how it functions. If it's an IO expander it should be extremely easy to figure out.