440 Oil Pump Won't Prime

This driving me nuts!
Swapping in a 440 motor home motor. Had to change the pan and pick up to car style ones, used a factory pan and factory style pickup which is right on the floor of the pan. Put new gaskets/seals in the pump while I was at it. I packed the pump with petroleum jelly to help it prime but got nothing on the oil pressure gauge when I spun it with the drill. Took the oil filter off and saw a small blob of the petroleum jelly pushed out of the housing and into the filter. Decided it was probably a mistake using the petroleum jelly so took a known working used oil pump I had, cleaned it up, new gaskets and seals and coated rotors and housing with oil. Put it on, still no oil pressure. Took the filter off and ran the pump with the drill again, there's a 'buzzing' noise coming from the outlet on the filter housing but no oil. I've used my cordless and corded drills running on high speed (counterclockwise), I ran the corded drill for 2 minutes and got nothing. The filter was half filled with oil when I put it on, the pan has 4.5 quarts and shows full on the dipstick. I’ve also cranked the motor with the plugs out, the oil light doesn’t go out and nothing registers on the mechanical oil pressure gauge.
Think it must be an issue with the pickup - anything I could be missing before I tear it down? The engine ran fine when it was pulled from the motor home