When I install a new oil pump, I check the side clearance of the pump shaft before I torque the pump. I just had a 406 recently with near zero oil pressure. I pulled the eng twice, checked bearings changed bypass, changed cam bearings, changed oil galley plugs...all of which were already new. Turned out to be a bad "new" pump. Installed a milodon STD pump and it idles 40 psi hot. The previous pump was a milodon high vol unit which had a defective bypass piston. Usually when psi near zero it is a oil galley or rear cam bearing alignment to changer issue so I am told.