My $3.57 -
Combustion gas blow-by adds volume to the gasses that the crankcase breather system has to evacuate. We have a 360* crankshaft and that means that the crankcases are seeing 750cc (or more) of volume increase or decrease every 180* but that back and forth so some extent cancels itself out, especially as engine speed rises and the time between highs and lows is reduced. What do the crankcases "cc" at?
We are not just trying to reduce crankcase pumping losses, we are also trying to (1) reduce windage losses to oil wrapped around the crank and timing chest what nots, (2) evacuate nasty combustion gasses from the crankcase, and (3) to help the oil pump scavenge oil back to the oil tank. We do not want too much vacuum in the crankcase because at some point that vacuum works against the oil pump.
Ideally the oil pump is scavenging ALL oil from the crankcase. It is a dry sump engine after all. But, at some engine speed(s), the high side outpaces the low side, resulting in too much oil in the timing chest and crankcase.
The '72 rear crankcase breather under such condition floods with oil and then cannot breath properly. It then is pushing oil up and against gravity through a small diameter hose, albeit with pulses of 750cc (and more) of swept area pushing air up and out that small diameter hose of far less volume than 750cc. It's like an elephant trying to inhale AND exhale through a soda straw.
The CNW reed valve helps that rear crankcase breather to evacuate gasses AND oil by converting it from a two way street to a one way street. Now it is exhaling only. Now the crank and timing chest whizbits can spin without ropes of oil hanging onto them.
So, I thiink that the '72 breather evacuates from exactly the right spot and all it needs is a reed valve.