I myself, hate taking a bite of a shit sandwich made by others. I would treat this as a stock 700B coming in and would install new back planes/output transistors, and a control board along with ALL NEW WIRING. It's the only way I could warranty my work since I didn't build any of it. Plus, we don't even know whats wrong with it. It can take many hours of troubleshooting and with the great price of White Oak boards, it may be easier to just replace them. Yer looking at about $1200-$1400 but it would be new with full warranty. I'm sure it's NOT what you want to hear. Or, I'd give you a credit towards a unit I have just completed. If you paid over a grand for it, I'd return it for sure. Bargain basement WOPL's don't exist. If you paid less than a grand, it's worth rebuilding. That's just my take on it. There are a few other builders here who may see it different.
Perry