Thanks Wilba,
I should've mentioned it's got the low level LCD and I was planning to use some 6581's. I tried a different power supply that outputs 12VDC regulated at 1A. Same problem. The new one puts out 11.92V so the DMM readings above are all the same with the new PSU, only a little less, that is:
Between the 2 J1 terminals: 11.92V
Between base board ground and J1 1: -.73V
Between base board ground and J1 2: 11.20V
All 12V connections to base board ground: 10.47V
All 9V connections to base board ground: 8.98V
All 5V connections to base board ground: 4.99V
I'm a novice at his stuff, and I don't understand the purpose of running a regulated PSU though a full wave rectifier. Is it to filter AC? Won't the output always be two diode drops below below the regulated input? i.e. isn't ~13.4 needed to give the 6581's the 12V they need? I can't thank you enough for putting together any awesome kit AND taking the time to help troubleshoot this kind of stuff.