Bluesman Mark gave us the answer back on page one. Even thoe the Barracuda was first, it was a REACTION by Chrysler Corp. to the news that Ford was coming out with the Mustang. The Barracuda was reaction to the Mustang, just like the Camaro, Firebird, Javelin, Challenger, ect.
Could it be thought that the Studebaker Advanti was the real first pony car? It fits the bill better than a "Valiant with a fastback roof" doesn't it?