You need a vented crankcase, actually a forced ventilation crankcase to purge
oil vapors from the crankcase, and keep the crankcase under vacuum. The
oil fill needs to be vented to let air in. Some vent these to the air cleaner through a hose for filtered air. The opposite valve cover has (or should have) a PCV (Positive Crankcase Ventilation) grommet or fitting. The PCV valve typically has a 3/8" hose connection that uses 3/8" fuel line hose to connect to a 3/8" fitting at the rear of the Carburetor. This distributes crankcase vapors evenly to all 8 cylinders. DON'T connect this to the #4 cylinder fitting on the intake manifold. This fitting needs to be connected to the power brake diaphram. If no power brakes, the fitting needs to be plugged with a pipe plug.