The Munch Mammoth had cast wheels in 1966, and Peter Williams experimented with them in the late sixties on his race bikes, but by the mid-seventies there were many choices. These are from Carroll Shelby's aftermarket company. The company must have been short-lived, I don't think I've ever run across examples of these anywhere. For American competition, Morris and Lester were selling their own versions. By the late seventies the motorcycle companies were all doing their own.