I'm working on a 67 shelby engineering car that has a lot of signs of being the blue 68 GT500 prototype fastback. It has this larger knee pad. Just wanted to find out if this was a Ford mustang production part or something unique? Worked on alot of mustangs and shelbys over the years and never came across this. If it is a production part, it would be nice to see just when and at what plants changes happened.