Google a 73 Scamp, and on a seperate tab a 73 Duster. Click on images and you can switch back and forth to see the difference. It's subtle. The lower body line on the scamp is more pronounced and goes all the way back more pronounced than the Duster. It kind of lightly blends in to the wheel well. It's the same on the Dart Sport. Not 100% sure body lines will match up perfect or if there some slight curvature issues. But there might be differences on the inside of the door... the cage. If I were tackling this, I'd keep it simple by getting a door from another Scamp. Just to be on the safe side. I never had to get new doors for mine. They were perfect. So I'm not 100%. But to me it looks different by the pictures... slightly.
I may be wrong on all of this, but I have a 73 Dart Sport, and body-wise I've only noticed really just the front clip I could use off of a Scamp. Even the pillars around the windshield are different (squared out instead of rounded at the bottom corners). So I've always tried to get parts from another like vehicle.