Boy, wouldn't he be feeling better right now if he had checked his clearances while assembling the motor! 15psi is enough to keep the bearings happy at an idle. but the discrepancy between as little as 15 & as much as 50 sounds odd. Personally, I'd run it until I had to tear into it again, then next time around, double check all bearing clearances.

I'll be interested to hear others take on oil pressure fluxuation like this. Some may say it sounds fine. For what its worth, my 110,000 mile original 1966 383 bottom end assembly shows 40 psi at idle and about 43 at cruise with 10w-40.