Being raised in the 60's, I remember the def. of pony car being long hood, short trunk, 4 seater, cars such as Mustang, Firebird, Camaro,ETC.
& muscle cars being the Fairlane, SS, GTO, SuperBird, Datona's, ETC. It was very explict in the 60's that Mustangs were Pony cars. Ok enough history...