Muscle cars are fine and all, but the only really good thing about them is the engine.
Brakes, suspension, chassis all pale in comparison to most tuners.
Radial tuned suspension on the old Monte Carlo. Held the track just fine. My old Chevy destroyed civics on short courses. Was a Caprice, not a Monte Carlo, but the geometry of the suspension was the same. Great brakes, wonderful ride, responsive...people don't give the old iron enough credit.
Well, a mustang compared to my STI for instance.
If both stock that mustang will eat my STI for breakfast on a dry strip. On a wet strip that reverses and I smoke him.
Then you have weight, and suspension (body roll) to consider. Negligible depending on who is driving, but same driver in both should do better with STI on a tight course.
Then with the GT 500 for instance the car will have severe brake fade after only one lap around Leguna Seca.
This is the sort of stuff I meant.