You said you had this built off a earlier non roller prevortec block. And your howards cam kit and roller lifters conversion, had everything required. The engine was rebuilt with new cam bearings installed? Did you confirm cam journal diameters to bearing id clearances? Roller lifter O.D. to lifter I.D. hole. (?) The oil at normal operating temp's ( oil temp, coolant temp) is not your low pressure condition. Where does oil travel? Oil pump, filter housing, block passages; crank-mains, rods; cam- pushrods. So alot clearances on the high side can add up. And therefore at normal temp, normal idle, the normal output of oil pump could not be enough for all the excessive flows. The other theory from what is described, could your oil pump be not up to the task- too many small leaks at low output, or could your pump have an internal problem, at higher rpm it's good but great. If the pump has excessive clearance or has suddenly failed internally ( broken relief spring) good at higher rpm crap at idle. Those are what i think about from your descriptions. For 100 psi and less i use a mechanical gauge with 3 inch face, goes 0- 100. The zero is at 7 oclock and 100 is at 6 oclock it's an OCD thing exact pressure indicate. Unless during the block overhaul some plugs were left out causing excessive pressure loss. Everything else is normal, no other unusual souds or actions. What i would do is probably, bite down on this it will hurt, drop the pan and swap out the oil pump. And see what happens, with no other indications, .....I'm not looking it up right now but the low oil press light comes on when oil press is below 6 psi? Okay good luck, please let us know your outcome and or what you find.
