Ok, the board from the 813a is 19323F.
I believe that's the part number, with F being their version, so the 813a's is a little newer.
I'm basing that on all the other components that Technology Research Corp made that are in the units. They're pretty much all 19xxx part numbers.
That's of course just two points of data. We would need to see the boards on some other machines to make any real conclusion. I would kinda doubt TRC will want to give us the answer themselves.