Either the Sig's or Balsa USA are easy to modify, Fiberglass Specialty sells cowling for the Supercub version, I've got the one for Balsa USA's, very well made, as a matter of fact it will be my next project after I finish painting a WWI biplane, aside from the nose area, the differences are in the shape of the stab and elevator and shape of the rudder, the addition of flaps will always improve your flight envelope and other visuals that you can gather from available photos on the web.