This was Norton's works racing bike for 1955, but AMC axed the works racing effort and it never got to a track. Sammy Miller has the restored original bike, And obviously someone has built up a replica here.
The original is shorter than this replica because it had special gearbox/engine castings to unitize things, which is why the clutch is so much closer to the crank on the period photographs.
After 1954 the Norton racing team used machines based on the standard production Manx often testing bits that would end up on next years over-the-counter racers.