I am really surprised that the engine was actually starved for oil. After hearing of what you found, I agree that with what you found, a complete cleaning will be necessary, and then you haven't figured out what went wrong. Did you look to see that you had a float on the oil pump and that there was no restriction in the pickup. There has to be a reason that you lost oil pressure and its almost got to be something wrong at the oil pump. The tang on the distributor is actually the shaft itself so if the motor runs, the tang turns. Are you sure you shvoved the oil pump all the way in so that the set screw went into the hole? I suppose I have guessed this whole thing wrong, but, I would really suspect that something went wrong coupling the distributor to the oil pump. This is why I am not a big fan of turning the pump with a drill. There is always a possibility of not getting the distributor stabbed correctly. And there is really no way of telling if a GMC distributor is stabbed all the way by just looking at it. I usually remove the plugs and spin the engine with the starter until I get oil at the rockers. One more thought, I think there is an upper and a lower bearing shell at the rear main. The upper one has a hole and if you don;t have the hole you starve for oil. But you would still show oil pressure on the gauge.
I recently blew a turbo on a Cummins and the driver didn't know to kill the engine. We didn't even bother to inspect the engine. Its going through an auction as a core on Wednesday.
http://berryhillauctioneers.com/detailview.php?itemnum=536793Cleaning up an engine that was starved for oil is an expensive ordeal. My Cummins will probably wind up in some country where they have cheap labor.
