The problem with the shaft adaptor is that most sellers do not know what the part they offer will fit?? You will see "fits All 54-63" on their ads
You need to go to a seller (specialist) who knows the difference between the 4 or more outwardly identical parts
The dealers who specialise in Gold Star parts should know what you need, or as I suggested SRM
I wish you luck in finding good "used" clutch parts !!!
The Triumph clutch inner drum that incorporates a cush drive is what you need, I have never found a good secondhand one, when worn internally they cause all sorts of clutch issues, DAMHIK !!!
Changing the bike to 12 volt will make the wiring much simpler as you can do away with the troublesome combined lighting / charging / ignition switch..
Royal Enfield (2 wire) alternator / rotor and rectifier regulators might be a cheaper alternative to the replica Lucas
parts. the modern stator will not match up with the old rotor..