socket size

I would like to buy a socket to fit the camshaft nut, and i suppose it also fits the crank gear, but since i don't have an engine open and the british wrench size make no sense to me coming from metric /usa background.... what size of socket do i need whitworth or however the call it ?

Get a good set of Whitworth sockets, you will need others on the engine anyway and cheaper as a set rather than built up from singles.

The manual says 9/16 Whitworth. I use 1" SAE.

According to the chart below the actual measurement of 9/16" Whit is 1.010" or 25.65mm.

http://www.baconsdozen.co.uk/tools/conversion charts.htm

FWIW...I think the worm gear takes a 1/2 Whitworth. !5/16 SAE fits but is a bit loose.

If your intention is to keep the Norton and do your own service work, then it would be best to buy a socket set and a combination wrench set in Whitworth. Removing the cam nut and the timing pinion worm gear will require a cut away timing cover or a tool like this: https://andover-norton.co.uk/en/shop-details/17035 or you risk buggering up the intermediate gear shaft bore in the case. The Gearbox has Whitworth as well. Buy the best what you can afford.
Cheers,
Thomas