Thanks for your help.
I'm pretty sure it is the driver board, likely the BCD to 7seg IC. During boot up, there is garbage on the display but it is bright and solid. It doesn't seem like it has outgassed. Once the MPU completes booting, and I believe begins sending the BCD signal to the displays, that is when it starts strobing crap. I am just guessing mind you

I think I'll try and replace the IC. A local collector has one for me. Unfortunately, unlike the PIAs, this one is not socketed, so my PCB solderings skill may be tested. I will install a socket to while I'm at it.
Diagnosing and repair this has been quite rewarding, now I'd almost hate to sell it.