Need a port for PCV.

History lesson (yes I am old). In the beginning there was the road draft tube to vent the crankcase ( atmospheric pressure at work). Then in the '40s came the PCV (Positive Crankcase Ventilation) using vacuum to vacate vapors and pressure in the crankcase. In this case the engine is still vented to the atmosphere. but we are pulling a vacuum on it. Then came the '60s (I love the '60s) we were concerned that these crankcase vapors would escape into the atmosphere when the engine was at rest (no vacuum). So we got the "closed system". Now we draw fresh air though the air cleaner. A PVC valve is a good idea, but where you draw your fresh air for is up to you. You can put a vented breather on the valve cover, creating an "open" system, or you can route that breather tube to the air cleaner.