My fresh rebuild, with a high volume oil pump produces 40+ psi cranking. If I remove the distributor and turn the oil pump with a drill, I get about 80 psi.
This is verified with a mechanical oil pressure gauge and the electronic sender from the Holley Dominator ECU.
This is with the oil hot from a oil pan heater using 20-50 semi synthetic oil.
How hot was the oil? I could hear the oil start to boil when I pulled the distributor. I quickly unplugged the pan heater. Lol
Did you prime it using a drill?
Did the drill start feeling like it had heavy resistance to spinning after the engine built up some oil pressure?
On a new working engine with a new pump, the drill will about stop due to heavy resistance (due to the oil pressure build up)
The drill needs to be a 1/2" drill set on low speed in order to get the pump to prime and move oil. It takes 60 - 90 seconds or more to get oil flow and pressure. The drill needs to turn counter clockwise.
Look and the numbering on the distributor cap or firing order.
The HO firing order is 1-3-7-2-6-5-4-8.
Non HO firing order is 1-5-4-2-6-3-7-8
You said you replaced the front cover gasket because of a leak. By front cover are you referring to the timing chain cover that the water pump bolts to? If so are you 100% sure you did not drop any of the old gasket material or sealant down into the pan? Only asking as it sounds like the oil pressure gauge used to work and since that timing chain cover reseal it no longer is showing pressure.
How many miles is on the motor? If you are getting alot of oil coming of out where the PVC check valve installs could be blow by which is indicative of a high mile motor. Also assuming the dip stick is reading full? There is supposed to be a PVC grommet and they can get hard and cause things not to seal.