Kartwheel68
Husqvarna
Pro Class
Just for reference, the operating section of the AHRMA rulebook.
The exceptions are bikes that are "like design" like the '75 250WR, and components from those bikes. Any other bike newer than '74, even if its essentially identical to the prior model like the '75 250CR, are not legal.
11.2. m) No major components may be later than 1974 (i.e., frame, fork, engine, gearbox, wheels, etc.) The burden of authenticating is on the rider. Press clippings and photos with identifiable dates may be helpful. Premier machines are restricted to Premier-type frames. Period modifications are allowed on all standard legal frames. However, no parts of later-period frames may be used for those modifications.
The exceptions are bikes that are "like design" like the '75 250WR, and components from those bikes. Any other bike newer than '74, even if its essentially identical to the prior model like the '75 250CR, are not legal.