rebuild 4.3 with low (no) oil pressure

'88 GMC Jimmy with 4.3 just rebuild. The motor was assembled, timed, and road tested fine. The next day when I went to adjust the valves for the final time, I noticed that there was no oil "squirting " from the push rods. I replace the oil filter, removed and blew through the oil lines, and checked for blockage in the oil galleries, and down the oil pressure sending unit hole. I aslo removed the remote oil filter assembly from the engine, and the plug on the side, and checked for blockage there. NOTHING!I have had the oil pan on and off four times checking different oil pumps including the high output one that's in there now.So right about now, I feel a little :confused: and :mad: . But that's not gonna solve anything. And yes, I have tried all the other suggestion that I found in the other posts that applied to my issue!

TIA for any helpfull hints, . . . .djontime

Pull the distributor, then using a distributor rod on a cordless dril, spin the pump. Oil should come up through the lifters.

Thanks for that one, but I've already done that. I have a modified distributor with no gear on the end removed. Using that and a mechanical oil pressure gauge, I end up with about 4psi.

You have had 4 different oil pumps that didn't build pressure? The odds of 4 pumps being bad are huge, so you must have an internal leak that is allowing all the pumped oil to flow right back to the pan.
Look at the oil bypass valve in the block, above the adaptor; is it stuck open? or missing completely? You say you are looking for a blockage, but that is not what you should be looking for. You should be looking for an internal leak.