oil pressure and different weight oils

Volume is WAY better for your motor than pressure.
Also, the size of oil galleys make no difference in pressure unless the pump can't keep up. (Lets assume the HV pump is fine)
45 pounds cold sounds like it would be about right with those lower end clearances, and like I said, volume is more important than pressure overall because the more flow of oil you have over and between parts the cooler those parts run.

Personally, I'd put 20-50 in it and call it good if it idled hot at 20-30 lbs