front quarter panels interchangable

Are you referring to what is commonly called the front fender? (PL-305 in the link?)
Demons and Dart Sports were basically Dusters with Dart Swinger front sheetmetal. '73-'76 Darts (including Sports) had a separate header panel in front of the hood. '73-'76 Duster hoods extended to the front of the car and didn't use a header panel. That said, I don't know if the fender (PL-305) listed in the link would match up with your hood and header panel. I actually doubt the length of the fender and the slope at the front are the same. You could actually put the whole front clip from a Duster on your Dart Sport but you would need hood, fenders, grille, and bumper to make everything look and fit right.
Maybe someone here has tried using the fender only and will chime in.
If I'm not mistaken mopardrt is referring to the 'rear' quarter panel from the door to the rear bumper.
BTW, Welcome to FABO!
Dallas