understanding a low oil pressure 360

By saying the gauge is “good” means you put a different one on and it confirms the low pressure? You can get a bore scope and look through the oil drain back in the head. To see how much “leakage” you have at the lifters, but can you really say “that is why” by looking at it? One thing that is somewhat easy and cheap is changing oil and filter. Go thicker oil, if the relief plunger is stuck open on the pump. Pressure might not change at all. Then, you could pull the pan, pump. Also plastic gauge a main and rod.