With B18 there are basically 2 types of crankcase ventilation control. Not counting the early one up to about 1963 which was basically an open circuit. After that the flow went one way and then it was changed over to the opposite direction to improve emissions. No PV came with the latter type originally AFAIK. If you have a hose from the oil filler cap to one of the filters that should flow clean air into the engine in a proper late type system and not oily fumes into the filter. Many of these engines, B18 and 20 have a mixture of the two systems so they don't vent as they should. Check the flow diagrams for these engines and see how yours shapes up. They are designed to keep a very small vacuum inside the engine and fuming should be minimal in a good engine. Properly set up, if you put your hand over the oil fill opening it should suck. Blowing means too much internal pressure so the PCV valve either blocked or fitted the wrong way round. there are other reasons. I think that he B16 has an open circuit so fumes just come out downwards through the side tube. Back in the day it used to be very common to be following a car and see these fumes pouring out from under the car. Rare now days and a sure sign of a problem with that car if you do.