Oil pump priming question

If it’s not behind the upper cam timing gear, the fault probably lies with with a pickup tube that is pulling air or is partially blocked by debris (I am thinking of cellophane/plastic wrap, had family in once from S.D. drive down on a fresh rebuild and they lost oil pressure at once. I pulled the pan and lo and behold...). It could also be the oil pump to main cap mounting surface is warped or the gasket is missing. This is also assuming that bearing clearances are all within spec and that it’s not a dreaded “diamond stamped” block that requires the .008 oversized lifters with standard sized lifters in place.