This is a 4 dr sedan conversion, which is the same as a two door in every respect except the doors, the roof is even the same.
In one picture you can see where they welded the convertible windshield frame on. The doors are different from hardtop at the vent window top, but can be modified. The floor is the same except the rear floor pans, and the trunk floor is the same except for a couple of extra body mounts. The complete inner side wall from door to tail light is different, and there are extra supports and braces around the top henge area. The trunk henge area is a little different, but all of these panels are available to buy new.
The difference in the frame is an x member that is welded in and two flat pieces welded on the bottom of the frame rails, all of which is also available new. All the frames are the same except for body mount locations and the x member on the convertible. You can get everything new, or even a new assembled body.
If you order a catalog from CARS it will list everything you need to make the conversion. But after you do all the metal work, then there is a lot of stainless steel trim that is specific to the convertible and very expensive.