a 650 pan actually gives more oil capacity which is a plus, many racers use it on 500/550s, but like brent said, you need the longer 650 oil pick up which will have the nipple for the hose too, should be cheap though. if you are lucky and the engine was run with high oil level, maybe the pump still managed to pick up oil and no damage was done. if your cam journals show any abnormal marks then it is a sign that it was run without enough oil.
but the only way to really check the health of the engine would be to do a total dissasembly and to visually check the main crank bearings for damage.
sorry for the bad news...