If it split 5.5 inches back, I think I would just plane it down from there, and then make your billet long enough to get it back to where it would match the rest of your arrows. Don't forget to allow for 1 inch for the taper on the end. By the way..if you have a tru center taper tool..you can use the little round guides that come with it when checking the diameter of the shaft after you begin shaving down the billet. If not, a caliper works well, and if not that...you can get it really close just by feel.