Engines with a PCV setup instead of a road draft tube had a tube from the "clean" side of the carburetor air cleaner to a nipple in the valve cover. That's called a "closed" ventilating system. California was one of the first places where the tree huggers demanded that no crankcase vapors could be vented to the atmosphere.
Jerry
PCV (positive crankcase ventilation) is the best thing you can do to upgrade these old engines. As Jerry stated, unless you've got some road speed road draft = crankcase oil diluted with fuel, blow by, etc. There is a reason pcv systems were being used in many applications before it was mandated by CARB (California air board) or DEQ.
