I am using a 74 frame on a 78. The only 2 things I noticed so far are
the rubber seal undereath is slightly different , the hole for the ws motor wiring is on the opposite side ( not a big deal ) . You might as well get the older rubber. The other thing is that I have to rewire the ws motor (not a big deal). The vents for the defrost are different , but they don't make much difference. All the hinges and the hard top bolted with no problems. The glass is also different size. I don't know if I am missing anything else. Also in my opinion they are much stronger and better looking than the newer ones. Also make sure that ws motor is in good working order , because I hear that they are hard to come by.