I wouldn't think there is a single difference in the roofs from 67-76 with the exception of maybe small brackets for the different headliners (cardboard vs. cloth, or maybe the later roofs that had an option for a moonroof which might have had different bracing).
Were are you located? I have a 70 Dart Swinger shell I have thought about cutting up since I need a few pieces off of it. I'd consider it, but you'd have to pick up the roof in IL. Also, if you just needed the center skin, I have a 4 door that might do the trick without using the edges (this roof is completely different otherwise unless you have a post car).