Thats to big a diff.if the valves dont clack you may wanna ck the valve adjustment.to make sure that thay have not been bottomed out in the lifter its a trick people use to hide in a engine that has low oil pressure most likly you have to clearance in the main and rod bearings..if the lifters have been bottomed out you have u have alot more problems cam n lifters...if not motor out turned crankshaft new bearing-and u can get a 80 psi oil pump normal oil press on a rebuilt engine should be 30-40psi at 2000rpm if not its not been built checking clearance.And the oil press in a pontiac is at the rear main bearing gallery oil has to travel though the rest of the engine and engine is not have enough supply of oil .seen it many times my press cold 80 psi- hot2000rpm 60psi-idle 35psi..30 year Pontiac man...