Nice bike.
Gearbox you may get from George Yeomans or Hawkshaw, if not, stick a Triumph pre-unit box in and make up a tin primary (which it had originally anyway).
You've got all the tricky bits really.
If it was mine I'd use and adapt bits to get it running and enjoy it, rather than go for originality.
Pre-war bitzas are the new craze, it seems, and a good thing too.
Much more interesting than someone boring us silly with tales of how their 1987 Yamakondazumi 125 is the new "classic to have"....
