318 with blow by

If you are using some sort of aftermarket valve cover without a baffle, your PCV may suck oil. But, if the crankcase is building pressure, your rings are shot (and the engine will leak oil like a Lycoming). Do two compression tests, dry and wet. The wet test follows the dry test, shoot about a teaspoon of oil into the spark plug hole and retest. If the compression number is higher, this confirms worn rings.