Bob Farnham tuning in the UK removes the clutch to re-drill the crankcase to accept the newer 13mm (1/2") outlet.
The increase in outlet diameter might not seem much but you have to consider the area, not just the diameter. Doubling the Diameter increases area by four times.
6mm diameter breather pipe area = 28.27mm2
13mm breather area = 132.73mm2
Earlier bikes, up to VIN number 221608, had their breather hose outlet spigot attached to the inner pipe/seal assembly, like this:
Later ones don't have that pipe and the spigot is just a push-in fitting I believe. Not sure how it's held in the crankcase.