I was wary of trying the wrong board in the printer, so I emailed the seller and he also had a 350 pulled board. He said that he also encountered the same error code in the past, and swapping the board was the only way he managed to fix the problem.
Sad, as I feel all that is wrong with the motherboard is some whacked state that could be cleared if only I could find the documentation.
Perhaps it's in the service manual I ordered, but I doubt it, since Xerox support could not find it in there..
Thanks all, sorry to have ranted in public here, I will now shut up about this and get some work done..P-)