Been thinking about this, it would require some research. But you may be able to find a 23" rim set up that already works with 35mm forks. I had looked into doing this. For example the xl250 utilized 35mm forks and had a 21" drum wheel. I know your set on doing the 23", but you may be able to find a wheel/fork combo that has a 23" wheel and 35mm forks and just swap those forks into your xs for a direct fit. At least that way you wouldn't have to make spacers and figure out a brake set up on your xs forks.