Maybe this will help........A friend of mine wanted longer risers on her VTX so we got some Valkyrie risers.....they fit ok, but the theaded stud that goes through the tree is shorter on the Valkyrie risers. I almost didnt mount them for that reason, but I got almost the entire nut engaged.......the end of the shaft was just shy of extending through the nut but it tightended up fine. So going the other way you will have excess bolt and the risers will move the bars forward and down a tad, but otherwise will fit fine
A good standard to follow is;
The minimum thread protrusion for male threaded fasteners is one full thread beyond the face of the nut or plastic insert of self locking nuts.