This is just my take on it for a road car.Vented oil filler cap and no other breathers in the rocker cover.All other breathers to a sealed catch tank.Output of catch tank to carb inlet,all sealed.A pcv valve would be a nice addition(google it)
if the blowby passed the rings is severe enough to leak past the clutch seal you could be changing this daily and still not curing it.You are looking for a slight vacuum in the crankcase.Road engines have not vented to atmosphere for decades and it is not just environmental concerns.
I think it was General Motors who perfected Positive Crankcase Ventilation(pcv) and did not patent it as they wanted everyone else to benefit from this.
At the end of the day you do what you have to do,Steve..