I'm in the wrap-up now! I worked a bit on the "move the bugs" routine.
The set-mode was in a sequence of mis-aligned dissassembly. It sets 128x96, 4 pixels per byte.
I was looking for the graphics format, but I'm having a hard time finding the code that sets it. Maybe the emulator will help ... tell me what's written to registers and when.
Best I can tell by web search and youtube, the graphics mode is 128x96 Color Graphics