Some of the best motors I have had came from left over, used parts. You have nothing to lose with them. We had a 355 sbc that was all used, mismatched parts. In the winter we would just back off the valves. Come racing season, tighten valves and check the oil. That motor ran for 3 years in stock body 81 camaro with 1 fiberglass hood. It ran 11.20's all day long. The car got sold. The new owner changed the oil. The next time out he blew it up. I told him not to change that oil :lol: