416 low oil pressure at idle
When I mocked up my stroker I ran the oil pump with a drill and turned the engine by hand with the intake off. Oil squirted 8 feet in the air out of lifter bore at max lift. Had to have a custom ground small base circle cam to correct the problem (special thanks to Brian at Indio Motor Machine). This was with a hydraulic retrofit roller cam and Crane roller lifters.
My point is mock the engine up and run oil pump with drill and check for leaks both under and above the lifter. Factory blocks are very sloppy so this is a problem on some blocks and not others.
Glad to hear original poster corrected the problem instead of ignoring it.