Duster 340 not a muscle car...

"1970 Model Year Musclecars"

'Big Blocks Only'

* Plymouth Road Runner
* Plymouth GTX

* Dodge Coronet R/T
* Dodge Super Bee
* Dodge Charger R/T

* Chevrolet Chevelle SS 396
* Chevrolet Chevelle SS 454

* Oldsmobile 4-4-2

* Pontiac GTO

* Buick GS

* Ford Fairlane 'Cobra Jet'

* Mercury Cyclone GT

* American Motors 'Rebel Machine'

The term is subjective. In my opinion musclecar means any sedan or coupe with a factory built high performance drivetrain and marketed as a performance car.