if you dont have a restiction like pro says then a open in the oiling system would do the same thing. if you left a main bearing cap loose then you would loose most of your pressure there. so while your looking for a restiction look also for a open. a plug in the oil gallery left out. main or rod bearing cap loose. if a lifter comes out of a lifter hole you lose most of your oil pres. oil pump loose, or pick tube has a hole in it. did you put in new cam bearings? i think you can put the cam bushings in wrong and loose the oil pressure. not saying anybody did anything wrong but these are some of the things i would look at. ive been told if you have a problem go back to where you just went and most of the time youll find the problem, and it been true most of the time. do like pro said take the drill and turn the pump again and see what happens. oil should come out of the push rods that way like it would with the motor running, but if its not you might can hear where your loosing your pressure