What block? I have a proto type R3 block that had no oil returns in the lifter valley. I drilled 8 3/8" holes for drain back. It still is dropping oil pressure at the last 100ft. I've run it like that for 5 years, no issue. If the level is too low the pump will start sucking the pan dry. If the level is to high the oil becomes aerated and your losing the hydraulic wedge between metal components. That being said I've been running my 572 @40 psi through the lights. Checked the bearings, there OK, but I've just restricted oil to the upper end to reduce the internal leak. This will send a greater volume to the lower end. Thick oil is a band aid. It raises PSI but not flow. Flow is what cools the surface of the bearing.
Doug