I've had a Power Mac Upgrade Card in my stash of expansion cards for a long time with no computer to test it in, but I recently grabbed a Quadra 700 which should be compatible. The Quadra works fine and passes all the MacTest Pro logic board tests, and will also boot with the upgrade card...
I recently came across a Quadra 840av that was in a pretty sorry state after 20 years in a damp garage. I asked the seller to test if it was working and he said it more or less exploded when he plugged it in.
I still decided to buy it for $20 in case it was repairable, and the logic board...