Barrel swap,

I read somewhere it possible to put a 750 commando head and barrel on a 650ss has anyone done this? Thanks

If you have a 650SS, you can get more power by revving it higher. I suggest it should be able to rev safely to 8000 RPM. A Commando motor probably relies more on torque. Gearing has to suit the power characteristic.
I cannot remember if the twin carb Manxman was a 650SS.

I was asking about inter changing parts, not how high it would rev!

https://www.accessnorton.com/NortonCommando/600-and-650-and-ss-and-atlas-engine-differences.31988/

The search function can be your friend.