Here are a few tips for you for a factory GT. First of all the engine code in the Vin number 5 digit, must be an "A" or "K" code. Both mean Factory 4V, "A" code is 289 Challenger Special 225hp, and "K" code is 289 High Performance 271HP. This is a "A" code 289 Challenger Special car. All GT's had Disc Brakes up front, as does this car. Only GT cars had Dual exhaust unless it was a HiPo. GT cars dual exhausted exited out the rear valance, with Exhaust Trumpet Tips. GT's had special optional 3 racing strips down the rocker panels of the car, Special GT badges and M U S T A N G letters on the fenders. Also they had GT Gas Cap. They had Fog Lamps also in the Grill area. They could either come with standard Interior or Deluxe Pony, this car is Pony interior. Also they had a quicker ratio steering box, and sightly upgraded suspension. So how do you tell a Factory GT. There are really 3 different ways to tell. 1st if you have an original invoice that is a good way to start. 2nd, the rear frame rails in back, have some reinforcements in them. If you look underneath the car in the rear, and look at the bottom of the framerail, on the bottom right infront of the rear spring shackle, you will see a small hole about the size of a dime. If you stick your finger in it, and feel back toward the shackle there will be a vertical reinforcement plate that will stop your finger, on both frame rails. It is about an 1" back. If there is no stop in there, you have a clone, only GT Dual Exhaust cars had this reinforcement for the exhaust hangers. This car has them on both sides, and has its original frame rails. Here is another key, turn on the fog lamps by themselves, if the rear tail lights turn on, with the fog lights you have the correct wiring. Many people when they try to clone these cars don't realize this.
David