Even with some custom machining, I believe installing the readily-available V8 pump gears will be less expensive than trying to find the relatively scarce GMC pump. The modified pump should provide about a 20% increase in output volume compared to the standard pump. That should counteract the effect of increased main and cam bearing clearances on a well-used engine without going to the effort of a full overhaul. The concerns about "seal leakage" are just silly- - - -none of the seals have direct oil pressure applied to them and it would take a massive amount of splash to create any sort of a leak from a seal that was not worn out already.
The "14 PSI" quote for the oil distributor is the MINIMUM pressure required to get oil flowing to the squirter tubes for the rods, not some magical maximum that will cause an outbreak of Bubonic Plague if it's exceeded! That is to assure the other bearings get oiled on startup, before oil begins to flow to the rods. "75 PSI" pump relief valve?- - - -I wasn't born yesterday!
Jerry
