[Ronnieroadster]

One mistake even a veteran will make I know from experience decades ago is installing the oil pump idler gear backwards the gears will mesh but have ever so little engagement that wears away quickly then all of a sudden no oil pressure. Heres another example. One time on a fresh build prior to starting I tried to get the oil pressure up no matter what I did no luck getting any oil to flow. Finally removed the oil pan removed the new oil pump looked up into the pump hole and with help turning the engine in the front looked into the pump hole discovering the idler gear was not turning. The cam I used was a NOS 8-BA cam. When I removed the cam I found the gear on the end of the cam had fallen off it was sitting in the oil idler gear compartment. The cam did not have a flat area to hold the gear from turning so not all late cams have that flat that NOS gear was extremely loose never expected something like that to happen with a cam I removed from the factory applied cosmoline and burlap type covering. If you could remove the oil pan and look at things that should help you figure out whats wrong.
Ronnieroadster