If wear in the throttle body journals is less than 0.010" you could drill the bores 0.010" oversize using a "P" drill (0.323" diameter) in a drill press, and install a 0.010" oversize throttle shaft. To avoid drilling out the throttle arms you can turn down the exposed ends of the throttle shaft to standard size (0.3125" diameter). If you subsequently return to standard size throttle shaft the original arms may still be used. Where the flexible shaft connection clamps will fit between the dual carbs, the shaft ends need to be turned down to standard size to fit the clamps. This area is not as critical as where the arms ride, so you may be able to do that with a file and the shaft spinning in a power drill. Some replacement shafts are generic (universal) and may have extra length. In that case one of both ends may need to be cut back to length of the original shaft.