Well, as it turns out - the one piece of Professor Pacman hardware that I didn't emulate is used by D&D. The good news is - I got it working tonight! Now profpac passes all self-tests, and demndrgn runs into the game portion. I need to map the controllers and dips now, since I can't control the player yet.
Right now there is no sound, but it sure seems like it was supposed to have speech! There is a part where a wizards head fills the screen, and his lips move. I wonder what's up with that?