1974 Duster t-top conversion

Well, the factory made convertibles. They rolled off the assembly line with torque boxes, so, I'd stay that would be a good start. Subframe connectors would be a good addition from there. You could also look into reinforcing the rockers, or tying them to the subframe connectors in a few places.

Don't forget that reinforcing around the T-tops will help too, you need to tie the existing hardtop structure into the T-top frame. Obviously you're going to be adding the T-top structure from another car to the Duster, so there's going to be a lot of custom work. And how you tie the t-top structure into the existing roof structure will be important. Something as small as some additional gussets between the roof structure and the T-top structure can make a big difference.

I kinda hate to admit that I've actually thought about this. Kinda like how I hate to admit I've thought about adding a more modern sun roof more than once. Sorry, I spent more than a few years driving a roadster and sometimes having the sun shining down on you is just a nice deal. At this point I wouldn't do it to any of my Mopars, too many hassles with leaks etc. But I get where you're coming from.

The bottom line is that if you have the skills to graft the T-top structure into the roof line, matching those curvatures etc, then you have the skills to do the chassis reinforcement. Honestly the chassis reinforcement will be easier.