OK, I'll see if I can help you. I have a 68 coupe and a 69 hardtop. Here is what I can tell from looking at them. First and obvious is the post. It looks like 3 or 4 spot welds at the top and 4 spot welds at the base to get the post off. The door jamb panel (where the striker mounts) is different. The hardtop has a cutout for the rear window to come up out where the coupe does not. The upper interior rear panel is notched for the sedan. The hardtop is straight. The upper trim piece is also notched to clear the post on the coupe. The door glass is different. The hardtop has a trim piece that butts up between the quarter window and door glass. The glass is also shaped differently at the top rear. Then there is the window mechanism, and the various stops and brackets. There are fuzzies to seal the rear glass to the quarter panel. And a different rubber seal at the door jamb to close in the rear window opening. Lastly, you will have to pop a hole in the door panel for the window crank and add the crank.

I think I covered it.

If you need pics, let me know.