Hi Rocky
   The plug type radiator cap for your tractor is not the right one. That means the radiator top tank is not right either. The last tractor to use the plug type radiator cap was tractor serial number 37496. Tractor 37497 and up should have the winged cap. This change was made in 1927 on the G series 12-24.
 The parts you should have follows:
13032  top radiator tank
13028  Radiator cap filler ornament  ( Wings)
13027  Radiator filler cap   (oval cap Wings bolt to it)
13029  Radiator filler cap clamp. (bail that holds cap closed)
13119  Radiator cap gasket plate   (oval plate fits under cap and holds        cork gasket in place)
13030  Hinge pin (can be made from round stock)
     Hoov