Use a long hex rod to check the feel of the oil pump once it has been torqued onto the block. Sometimes the oil pump housing will distort and bind up the gears. In your case it should be fine since you had run it before, but who knows. Might have been a bit of extra resistance coupled with a weak shaft.
I think you are mentioning a possible block error (like Al ) that the oil pump machined pad isn't perfectly aligned with the shaft/bushing in the block.
I have primed the engine many times in the past couple weeks with the oil pump bolted up and the drill "felt" normal turning the pump.
