[A1971Blazer]

Something I ran into years ago on a motor I built....

when the machine shop installed the cam bearings, they failed to get the rear bearing all the way in to the proper position....

there is a radial groove under that bearing where oil goes up around it and the up into the lifter galley......

if that groove isn't covered by the cam bearing , most of the oil will just pour out there and run back into the pan....the motor would run, just didn't have much oil pressure.

not saying that's your problem but it happened to me.