Yeah I'm standing by my opinion. Like I said, the term "muscle car' is only going to be personal opinion but the 57 Chev I would class as a classic car, not a muscle car.
And yes I think to be a muscle car it has to be a two door. You can get tough cars in every variety but that doesn't make it a muscle car. I wouldn't say an XY GTHO is a muscle car as it has four doors. Yeah its an awesome car but its a sedan. Just like how the new Skyline is an awesome and tough looking car with only 2 doors but its no muscle car.
A fuelie '57 WAS a muscle car! Like it's rival the McCulloch(later Paxton)supercharged '57 Ford Fairlane. The muscle car did not begin in a blinding flash with the '64 Pontiac GTO in the US, but was slowly evolving from 1932 with the FORD V8 , 1949 OLDSMOBILE ROCKET 88, 1951 HUDSON HORNET,1951 CHRYSLER NEW YORKER/SARATOGA FIREPOWER HEMI V-8 ETC.Look at the Standard Guide To AMERICAN MUSCLE CARS, all these and many more are listed.