understanding a low oil pressure 360

I see now where you said you didn't measure the bearing clearance. That's a big no-no and will be extremely difficult to keyboard diagnose without knowing that. One other internet "mopar guru" built a 318 recently that went for a famous online dyno test, and he assembled the engine with std bearings, and a .010 under crankshaft, and it had low oil pressure also. Could be cause