Hi
The cheapest rotary Norton's on the market are the ex police
commander or Interpol 2. The Interpol 2 start from £800 for an air-
cooled to about £2.5K for a commander. The only problem with using
one of these bikes is the gearbox can hardly cope with the 65 hp and
once you put an ejector exhaust on you will be up to 100 hp easy. The
engine would be ok. There is a bitsa of a race bike on the market at
£15k that has a commander type gearbox.
If you can find a f1 for sale it would probably cost between £8k to
£12k depending on condition. A f1 uses a Yamaha fz750 gearbox I have
used one for 10 years without a single failure.
My friend has just completed a build of a f1 from bits so it can
still be done.
I don’t want to ask him how much it has cost though.
Good luck
Huw