On my '72 El Camino 350 with Autometer guages, the oil pressure guage is driven by a very small tubing from the engine to the guage. When starting up in the morning cold I get 50 lbs, when warmed up 25-30. When real warm and stopped in gear it drops to 10, if I put it in neutral back up to 25. Seems low but I'm thinking when you change the oil that little tube keeps the dirty old oil in it, so how accurate can it be?

Sounds very accurate. Chevy says 10 psi per 1000 rpm up to 4500 as minimum. Lower when hot is normal.