Getting closer ... Space Zap is now playable (but not perfect, shows up a possible problem with interrupts and expand function on the magic write) so I plugged in the rest of the roms I was going to look at - Gorf & Robby just give a black screen
, but Wizard looks pretty good as a start point - of course, it needs the sparkle circuit and stereo sound (and eventually a speech chip or samples), but gives me the next thing to work on.