I found the datasheet for the MSM6502 (stupid OKI, reusing "6502") and the good news is it has no less than FOUR test pins. looks like 2 in, and maybe 2 out. The docs don't say a whole lot about it, but it does have a complete opcode listing with hex values so there is that.
It's a later sheet (1986) so it cuts out most of the more interesting parts, but I think there's enough there to go on.
Connecting to the QFPs is a pain because you have to make custom adapters- there's no ZIF sockets for most of these non-standard sized chips unfortunately.
When I decapped Electronic Talking Battleship, the die got stuck in the top plastic and I toasted it pretty badly trying to get it free. Unfortunately, Whink didn't clean it up very well. The ROM bits look like they are possibly a little small for me to read anyway. It looks like 8K of ROM. Here are a couple of 5Kx5K GIMP files: www.seanriddle.com/electalkbshipmetal.xcf
hap: no prob. what does galaxian do? it just doesn't run?
btw galaxian does something neat with the VFD. when something blows up, it will stop scanning the grids and turn the grid on that is over the object that is blowing up, and hold it there for awhile. this makes it light up really bright for 100-200ms.