No mention whether the engine has a recent rebuild or if had been vatted. Before pulling engine remove the oil sending unit and take a straight piece of coat hanger or welding wire and stick in the hole that the sending unit came out of.About 4 inches down in the hole 340s have a small plug about 5/16s in diameter that looks like a small freeze plug which diverts oil to the top of the engine. Sometimes when vatted this plug comes out and the result is poor oil pressure. If the wire goes 6 to 8 inches down the hole then that plug is missing. Easy to check before pulling engine and can be installed from the top.Hope this helps!