73 duster interior

Under your hood, on the drivers side, there should be a metal tag with numbers and letters on it. This is what they call the fender tag, lots of info on it about the car. If it came from the factory with the fold down rear seat it should have C73 on the tag. All those alphanumerical codes mean something. They tell you what color the car is, if it has a vinyl top or not, what radio it left the factory with, etc. They called the Dusters with the C73 option "Space Duster". I don't know that they called our '73-'74 Dart Sport anything like that. Hope that helps, if you have any more questions feel free to ask, we'll all help each other out.
Galen's white books (must reading) calls it "Fold Down Rear Seat/Space Duster Pak. Ray