I have seen a fastback GT/CS Mustang before. It was just sitting in this person's yard with a wrecked rear quarter panel. The badging on it said GT/CS and it had the side scoops. I used to drive past this car all the time and I noticed that the rear tailights are not the same as a normal mustang. The car was white with red stripes and had a rear spoiler. Has anyone else seen one before?