The Honda spline is enough smaller that the hole can be drilled to give a smooth surface, the old spline teeth disappear(Barely). The Vincent spline has forty teeth, which is convenient because my milling machine dividing head is a 40 to one ratio, which many are. I mounted the kick knuckle in the dividing head with chuck facing up, spent some time getting things concentric, then mounted a tool steel lathe bit in the milling machine head. The lathe bit first had the appropriate grind for the spline angle ground into it.
Then it was a case of slowly scraping my way around the circumference of the hole. I used the power rise and fall of the table to make the cut. The lathe bit remained stationary. The procedure was ,make a cut, turn the dividing head crank one turn, make the next cut. From memory, the splines are only about .015 deep and .005 per pass seemed a reasonable cut, so three times around did it.