[Cal Metal]

My guess would be the Mustang. The Dodge Charger "fastback" design did not appear until 1966. It was based on the Coronet body shell. The '65 Dodge Charger was a Dart produced in very small numbers with the "Charger 273" name. It was not, howver, a "fastback" design.

Now, as far as a two seater is concerned, the '63 Sting Ray Coupe has what one might call a "fastback" design. But again, it was two seater, not a four.