Not an expert and don't know if this qualifies for an "official muscle car", but Back in 1970, my husband bought this car, AAR Cuda. It was kind of fun to drive. A real gas hog though.
TIS
"Mankind must put an end to war before war puts an end to mankind. War will exist until that distant day when the conscientious objector enjoys the same reputation and prestige that the warrior does today." JFK
A real gas hog though. 
