Bison, a billet shaft is not required unless the feed hole in the spacer plate have been drilled out from stock sizes, if duel feeding the direct(3rd) drum on a trans that has already "Had" the holes drilled from previous "Shift Kitting" the holes would need to be restricted(peened closed) and then redrilled to smaller size, when "Duel Feeding" both sides of apply piston there is no need to "Hit It" with oversized feed holes, unless you enjoy snapping shafts on 2-3 shifts with anything more than 135 psi line pressure.
Kevin.