Harry, I'm registered at enough places now, but it all depends on the winding length of the particular brand. He can figure the minimum winding length he needs by marking an existing string at the nut, removing it and measuring from the ball end to the mark. Then he'll need to check with the manufacturer. Unless something has changed recently, D'addario's shortscales have 32" wound length, 32 1/2" for GHS. Other brands will differ. Fender's 5250XL shortscale nickel plated steel roundwound set is advertised as fitting a Mustang. IIRC, LaBella shortscales won't.