If it's a recent rebuild and the builder used moly assembly lube you may have a cloged oil filter.If not your oil pickup tube may have fell off the oil pump.Make sure to put a tack weld on the tube were it meets the pump.
One way to tell what engine you have is to pull a head off and turn the engine so the piston is all the way at the bottom of the cylinder.Then measure from the top of the piston to the top of the deck.A 350 will measure 3 1/2" and a 327 will measure 3 1/4". Both engines will have a 4'' bore.Hope...
302 engines were small journal and 327 engines were small journals up to 1968.How do you see a small journal crank being interchangable with a large journal engine ?