I know if I was a better machinist, taking the crown race seat down to final dimension would be better done on the lathe. What I do is take it down close to the final dimension and then cut it with a crown race tool. Maybe when I get a DRO on the lathe I'll just go to final dimension on the lathe.

I have never had a steerer slip. Maybe I'm just lucky. I have seen people pin that joint, which always seemed to be a bit much. I like your fixture