OP

Quoted from DumbAss:

The test boards are compatible. The order is different. It's not a direct 1-1 incrementing or 1-8 decrementing for some of the different connections.
I did figure out a solution to this problem and got the board verified!

System 6 = Gorgar.[quoted image]
System 7 = Black Knight.[quoted image]

I ended up using my portable adapter boards. I had to find the ones with the appropriate key but didn't have one for the lamp rows. That's 9K7. So I re-used a connector and re-ordered the wires so I could use one of the available adapter boards I have to test the lamp matrix.

Gorgar is pretty straight forward. Solenoid firing order is not "down the line" on the panel but it is correct when order corrected.
Black Knight has the added complexity of solenoids 23, 24 and 25. I couldn't figure out where they go until I did some searching and it looks like 23 and 24 and not used and 25 is the flipper relay. 25 definitely enables/disables the flipper relay. The sound outputs also work. These are the pink LEDs on the panel. I connected them to solenoids 37-44 on the diagnostic panel.

I used the all-in-one EPROM adapter board so I could easily switch between System 6 and System 7. Actually, I broke a leg pin on my Black Knight EPROM so I pretty much had to use this board as I didn't want to bother repairing the EPROM. I'll do that later.
So, everything appears to work on the bench. My next problem is that I don't actually have a System 3-6 or System 7 game to test this board in. I know that the Rottendog MPU327 used to support System 7 but no longer officially supports System 7. I couldn't easily locate what the actual compatibility problem is so that's still an open issue for me. I have a small number of (bare) boards available and I will probably build another one or two to have available for testing. Local to the PNW and interested in helping out?
Observant readers might notice something different in the top left of the board. I have been struggling with this little thing for about 5 months now but it appears to work properly in this board. I hope to have some more information on this in the near future but it's been 5 months and it needs some more testing.