im sorry but i have to disagree, sports cars are defined by thier prowess to accelerate decelerate and corner. With the degree to which new challengers, mustangs, and camaros handle they are well beyond thier muscle car heritage. Muscle cars as defined (rightfully so) by top gear (outside source for "unbiased" opinion (lol i know)) are cars with big motors and crude suspension. Sure the ss454 was fast in a straight line but i wouldn't take one around a track were i have to turn the wheel. the muscle cars of old had poor weight distributions and didn't exactly stpp on a dime.
I also propose that the 1st z/28's werent muscle cars, but were instead Sports cars because of thier road course prowess instead of straight line ferocity.
with camaros and challangers that can pull into the .9's on a skidpad (something the ss's of old could not do) it means the SS is no longer just a big engine in a car. The camaro especially shows the finesse of a sports car without the limitations of a muscle car. Hence it is a sports car.