70's Duster Convertible

All Plymouth “A’s” and Duster bodies have shorter wheel base than Dart, so any Dart top frames would be too long. Duster has curved glass so top width would have to be shrunk, and convertible’s vertical post top attaches to and door glass seals to would have to be curved to match glass in door.
I bet modifying a curved glass midsized 70’s GM frame and top would be easiest path; which will still be a boat load of head scratching, and frigging around to make it fit, and fold into well without a bunched up mountain of a mess such as VW and RR ragtops have when top is retracted. Then there is the fixed quarter window to deal with; engineer and fit regulator some donor curved glass allowing retraction, a complicated project, or eliminate it and have no quarter window when top is up.

Then there is the back seat area reconfiguration to accept hydraulic pistons and top irons, and beefing up of unibody to withstand decapitation.

An interesting custom project indeed that can be executed by experenced builders.