71 Fastback Release Pipe Elbow (06-7878)

Yes, but only if you have made other arrangements for crankcase breathing, However when I did mine I added a reed valve breather but keep the timed breather as it does no harm having two. The timed breather is less effective at high revs but the reed one is still working then.

In stock at AN: https://andover-norton.co.uk/en/shop-details/17369

You can also drill a hole in the back of the timing case....details in Commando Service notes pg 12 and 14. In fact another idea is to use the Release pipe elbow in the back of the cases. But the crucial thing here is to realise the blanking screw for the elbow is the same as the clutch centre adjustment! But do NOT blank the breather off unless making other arrangements!!!!!

Was yours from the same bike or did you source a different one?

The Yamaha 650 one was never fitted to the Yamaha 650 ex factory, some enterprising person repurposed a EGR valve from a small Chinese motorcycle engine and marketed it as a breather valve. The best way to get one is on ebay, in Motorcycle parts search for EGR valve and pick one to suit where you want it to go, so the Yam 650 is a 90 degree one, there is a straight 180 degree one from a Yam 125.