John, as a reference point I started my 351 stroker for the first time on Friday. It's also a loose clearance motor with a Melling HiVo pump. I used Castrol GP50 20W50
oil. I primed the
oil system with a power drill attachment on the
oil pump drive. Just with an old drill, the oil pressure went to 75psi. We then refitted the distributor and when the motor fired up, the pressure went straight to 80psi and came back to 70psi when warm and 75psi with a blip of the throttle.
I ran it for 15 minutes, then replaced the oil filter and took an oil sample to have it analyzed just to make sure everything's OK. I fitted a cheper brand of filter and refired the motor, and the oil pressures were identical to the previous filter.
If you don't have access to a local oil analysis firm, I'd recommend replacing your oil filter and cutting open your original one to make sure that there are no horrible speckly bits lurking in there. If it only costs you a few bucks for the peace of mind, I'd say it was worth it!!!
Good luck,