Maybe you have a defective oil pressure gauge
All the stock and high volume oil pumps I've used with the black spring had 80 lbs. cold, no matter what weight oil (from 5W20 to straight 50 W) I used
EDITED: I like to see 10 lbs. per 1000 RPM with hot oil, IE 70 lbs. at 7000 RPM
I've built and raced a bunch of different stock blocks, 361,383, 426W and 426 Street Hemi as well as 413 and 440, most of them had loose liftrs bores and most of them would make 80lbs cold with a high volume oil pump, I've built them with .004+ main bearing clearances with the old Clevite full wide groove race main bearings with .003+ on the rod clearances.
I now use the Seal Power narrow full groove truck H.D main bearings that usually have a liittle less than .004 clearances with rod bearing clearances having between .0027 to .0035 oil clearance, I cut the bypass spring down, if needed, to get the 10 Lbs. per 1000 RPM with hot oil also if it has more than that after breaking the motor in