[Oldtruckfanatic]

Well the surging is likely ignition just as you suspect. The fact that it never warmed up tells me it probably doesn't have a thermostat in it at all and who knows why. Otherwise it would get to at least 160 or 180 depending on what stat it was. Regardless of the coolant temp it should have run within reason if the electric choke was opening. Its a beautiful truck but its that kind of trouble you have to look out for on any build. That thing could have anything from a bad distributor to a poorly jetted Carb to a flat cam and there's no telling what can of worms you're opening. If he wont adjust the asking price to reflect that risk its probably best to pass regardless of the open differential.