i just installed a rebuilt long block, and it has low oil lite on at idle.I removed the valve cover, and no oil is geeting to head. But, the bottom end, appears to be getting plenty of oil. Is it possible, for the head gasket, not installed right? I need to determine where the problem is, so i can contact engine builder. We ran and drove the engine for two hours, and no knocks, no sign off bad oil pump. any ideas? Thanks

Or the wrong gasket, thus blocking an oil passage up into the head? Or some crap that got down in a passage during the rebuild? I'd get back to the builder before you do any more driving.
Just some guesses.