You cant diagnose the problem over the Internet with out a detailed parts list.
What lifter and how much lump on the camshaft.To much lift you might be windowing the lifter skirt to the oil (you should be safe to .470 with most lifters)


When you dropped the engine off did you give them permission to completely disassemble and rebuild the engine ?
Try a different pump ?
Cranking the pump by hand you should see 40 to 50 psi if not the oil should be hosing out from somewhere.
you should only see about a 10 psi drop from cold to hot.