You are better off staying with the rad valve for that situation. Based on your power range specified, riding requirements and the fact you already have it. Boring your carb to a 36 would be good, if the diameter of the rad valve is a little larger but not necessary. I have one I can measure as I don't remember rite off. I had to do a lot of work on the last rad valve we used to get it to work well with a 39. Pwk to the point I wished I had a 5axis CNC mill. So I could copy it. It s doable to make them run good takes a couple hours of porting and in the end if your looking for mid top still maybe better off with a  billet manifold for straight 87-90 setups with airbox or Zilla  manifold on a 91-92.  The Zilla manifold turns the carb and is fine if you run open filter.