I am having a similar problem. I have a 1973 350 block with 1993 TBI & HEI. Completly reworked the block. I put a High volume oil pump in. New Cam .452 - 230 and Lifters roller rockers with 1.6 ratio. All new bearings, freeze plugs. It started just pine and said it had 40 psi oil pressure. I haven't even put it in gear yet. Maybe a totla of 4 min running. The first knock I killed it. I pulled the valve cover and I am getting no oil out of the valve covers. I did happen to notice a puddle of oil under the rear of the engine but thought it was the rear main. At a loss please help