So the '57 Bonneville doesn't count? All of them were fuel injected, using a similar system as the '57 Chevy (Rochester "Ram Jet"). How about the '58 Bonny with the 370 Tri-Power? They dominated NASCAR and NHRA in the late '50s through '62, when GM pulled the money... I 've never seen a '63 Impala 409 car that would TOUCH a Catalina SD car.
But the bottom line is the first true muscle car was indeed, the '64 GTO. The phrase was coined to describe that car. Chevelles didn't get REAL power until '66. The handful of '65 BB cars shouldn't be considered, as the L-78 was a RARE car. Same is true of Thunderbolts, Ramchargers, and all the other wannabes. At least GM sold their cars in volume, to the general public. MOPAR didn't really have a good one until the '67 GTX or Hemi Charger, but again, Hemi cars are too rare to compare. Ford NEVER stepped up in volume. It's easy to say a car built in low volume (less than 2,000 cars) can beat a true stocker. Let's see what cars were built in excess of 30,000 units, that could compete with the '64 GTO IN '64. Or 80,000 units in '65, 90K in '66, 80K in '67, and so on. Badmouth GTO all you want. It's still "The Godfather" of muscle cars.