Hi Keith,
I posted a while ago about my breathing problems. I picked up somewhere that the latest breather (same part you listed) opens at 90 degrees after tdc. That is what mine did. I found out by blowing through the hole in the breather valve. I had a degree wheel on the crankshaft. I then found that it closed again at 45 degrees after bdc. I think this is standard. I had another breather, supposedly the same part, sent to me, though. This opened later than mine. I have since made a mod that was recommended in an article by Roger Sharman of Cake Street Classics. This was to open up both holes, to the right, looking from the top - by 10mm. This probably makes it open at about 65 after tdc. I cleared out the breather pathways. I have a thick cork gasket that you can't shift (on the valuable play on the peg), by hand - with inner timing cover on.
It all goes well now. A bit of oil comes out the breather tube, which I collect in a bottle. That wasn't happening before, though - and crankcase pressure was building so the drive side seal would blow out. These mods happened at the same time as I put K-liners in the valve guides to cut that blow-by right down, though. So, I don't exactly know what is the main cause of the improvement.