We had this sort of problem once. It was on a 355 build. We took the engine apart 5 times changed rings, changed heads and it never corrected. What our problem turned out to be was that $5 PVC rubber grommet. The PVC area of the valve covers did not have a baffle inside the cover where the PVC valve went and the cove just had a simple round open grommet. The PVC valve was sucking up all the oil. A simple $5 cone shaped PVC grommet fixed the problem.