Jim is correct. The disk brake was introduced on the 750 twins and triples in 1973. Fitting a TLS brake to an earlier model is doable, using the triple trees makes it pretty easy and using the whole front end is preferable. Putting disk brakes on an early model is pretty difficult unless you use the whole front end. You can use just the triple trees but there are many mods to be done to make it work.
Been there, done that, got the check.
>Actually, the conical front brake was used only on the 650-750 range of bikes from 71 on until the disc ones came out......