The Mig-21 F-13 or Fishbed C is almost a totally different airplane than it's offspring. The later models have a larger, longer nose, a larger radar/nose cone, the canopy opens sideways, (the Fishbed D still opens forward), the speed brakes are different, the internal armament is different, the vertical fin has much broader cord, the main wheels are bigger, the 3rd generation has 4 underwing hardpoints instead of two, the nose pitot tube is on the top right instead of bottom and shaped differently, the braking parachute was moved from lower left fuselage to the base of the fin, etc.
The Revell Fishbed C is supposedly extremely accurate for a 1st generation machine, but it would be virtually impossible to convert it to a 2nd or 3rd generation machine.
I just bought an Aero Team Mig-21 UM, Mongol B, two seat trainer on ebay. I am anxious to see how accurate that is. The box art looks very accurate..
Darwin, O.F.