There's nothing wrong with introducing fresh air through a vented filler cap or slots in the valve cover, but it wouldn't pass the Commiefornia smog law. The system had to be totally closed so a really bad case of blowby went down the carburetor throat, not out to the open atmosphere. That system also avoids introducing dust into the crankcase since the air comes into the engine after the air filter does its thing. In really dusty conditions, that does make a difference in engine life.
Jerry
