[MrPbody]

I have never, nor will I ever, consider an Impala OR a Catalina (the base model of the 2+2), a muscle car. They are full-size performance cars. Same is true of the Furys, 500 XLs, Marauaders, Polaras, Ambassadors, Wildcats, Starfires, etc...
Again, we come back to the "my opinion" thing. The "definition" has nothing to do with "opinion", BY DEFINITION. If I weren't quoting from a book written by the people that were actually THERE, and saying "In my opinion", I would agree to the argument. John Z. DeLorean and Jim Wangers defined what a "muscle car" is/was. That is a matter of historic fact, not an opinion. Even Hot Rod Magazine, Popular Hot Rodding, Car Craft Magazine, Muscle Car Magazine, Motor Trend , and the list can go on forever, credit GTO with being the "first" muscle car. I don't usually site magazine articles for "facts", but my dad always taught me, "5,000 Frenchmen can't be wrong!" That means, if the majority in a given subject, all say the same thing, it's probably true...
The valves for the "nail head" have a very large head on them, resembling a large finishing nail. The valve angle is VERY steep, as pointed out. That led to the funny looking pistons with the big ol' knot on top. As we have learned over the years, the steep valve angle does not lend itself well to high performance flow characteristics. Chevy builders go to great lengths to "roll" the head over to decrease the valve angle (the primary purpose of "angle milling").
It is popular in today's society, to rewrite history to make it more favorable to a certain side of an argument, or to make it more politically palatable. Let the government and political parties muddy the water with self-serving BS. As technicians, we like to keep our eye on the ball. No matter how hard you try, you can't change the past. There can only be one "first". Why is it such a big deal to you, that GTO is that one?