When I first got my Comet the PO had removed the original timed breather, replacing it with a pipe sans valve to atmosphere from where the magneto should have been ( please do not ask how or why). After I reinstated the magneto and the generator I tried all sorts of contraptions in order to get to a oil tight motor and a breather that did not approximate a total loss system. I had excessive crankcase pressure and nothing I tried seemed to work. I tried elephant trunks, PCV valves, Bunn breathers and a hole lot more.
The solution was found after I destroyed a piston thru detonation. I fitted a new liner along with a new piston and rings (and sorted the carb and ignition). This eliminated all of the earlier "blow by" that was causing excessive crankcase pressure. At the same time I installed an original timed breather, modified as recommended by PEI - I opened up the "slot" in the pinion thus giving a longer duration when the breather was open. Being a Comet I have only one piston to worry about. I set the timing of the breather so it opens during the down stroke of the piston, and closes at 2 degrees After Bottom Dead Centre.
My timed breather outlet now goes into a catch tank (actually a discarded plastic drink bottle, painted black) and in over 2,000 miles of running there is around a teaspoon fool of creamy emulsion in the catch tank. Oil consumption is so low as to be un-measurable.
Just my experience