RUN- - - - -do not walk away from 5W-30 oil. It's approximately the consistency of water when it's cold, and it does not get "thicker" as it heats up. Try 15W-40 instead, or straight 30 weight. That being said, simply increasing the thickness of the oil will only hide the problem, not cure it. If spinning the oil pump with a drill motor doesn't solve the pressure problem, open the engine up and check for obvious leaks in the oil circuit. I once discovered the oil gallery plugs behind the camshaft sprocket missing on a freshly assembled 283. That one had no oil pressure whatsoever on startup and wouldn't build pressure by spinning the pump.
Jerry
