This is a new one on me, convertible???
...in fact, I do have a 1972 Charger SE factory 400-4 sure grip car with a badly rusted roof (and rusty panels elsewhere but a solid uni-body).
If I had easy/cheap access to a 75 and up Charger\Cordoba\Magnum T top roof, I'd do it.
I've seen that done to an E body 'Cuda (72 IIRC) and it looks like they should have come that way from the factory!
The Charger should be an easier fit.