So i have two oil pressure sensors in the rear port on the block. The OEM sending unit, and the aftermarket one from NVU. So i removed the OEM one and hooked up a mechanical gauge there. Pulled the distributor and ran the oil pump via the driveshaft, and i see ~40 PSI on both the mechanical & electrical gauge, so that confirms i have oil pressure when cold, and confirms my electrical gauge works properly. Drained the oil, pulled the filter, cut it open, and i dont see any bearing material. Brought the filter over to the machine shop since hes only about 5 minutes away and he agrees, no bearing material in the filter.
Today i changed the oil out for Rotella 15W40 (this time i put in 7 quarts instead of 6), ran the oil pump via the driveshaft and got ~48psi, which id expect from the heavier oil. Put the engine back together and fired it up. Ran it at 2k rpms for 4 minutes, and in that time it dropped to about 5-6psi so i shut it down. Waited 5 minutes, fired it back up and no oil pressure at idle. Shut it off, waited another 10 minutes, and fired it up again. Barely any increase in oil pressure. So i dont think its a problem with oil draining back down to the pan.
At this point i cant see anything else i can do, without pulling the motor back out.