its the inner panel that welds to the top of the windshield that is different on the full roofs, compared to the hard tops. The panel is repro'ed for the 69-72 gen, but I have not seen one for the 73-76 yet.
If you are keen you could make a fibreglass cap off the existing roof, like a carson top. As it would be in 2x pieces it would actually be a lot easier to remove, as they are heavy. You could even leave the "hoop" in, which would be a big improvement structurally, although I like the fully open look.
The doors are easy, as they are just stock doors with the top cut off and rubber plugs installed. I'm pretty sure the plugs are repro'ed.
Biggest issue will be re-inforcing the floor, there were 3 panels that bolted under the floor on either side to create a box section to strengthen the rocker ( stops the door gap collapsing when opening the door ). Pics are available through repro parts books, and they are straightforward to fab.
Post pics !!..