Have you checked to make sure that the oil galley cup plugs are installed that go behind the camshaft thrust plate??? I had a similar problem like this once before and that was the cause, the machine shop didn't put the cup plugs in the oil galleys behind the thrust plate...
Happened to me. I built a 360 LA. Motor would not pump up on left side.. Took out plug I installed and found one someone knocked it in about an inch. Luckily did not hurt motor.
