I'musually the last person to discourage someone from trying something creative with their car, but I really don't see anything good coming from this. But if you want to do it bad enough, it has been done. First, get both cars in the same garage and start comparing them. Find out what's the same and what's different. I think you'll find that the roof needs to be cut along the top of the quarters, all the way to the taillight panel in the rear, and I'd try to cut near the factory seam at the top of the windshield in the front. As far as bracing goes, oh yeah, you'll need lots and lots. First, make sure the doors open and close nicely on your coupe before bracing anything, then remove the doors and brace where they would go as well as across the rear behind the seat to keep the sides from caving in once you cut the roof off. I'd then brace across the trunk area and put a couple in diagonally to keep the whole thing square both front to back and side to side. If you feel you can pull it off, go for it. I've seen one for sale on ebay that was in primer and it didn't look half bad, but it didn't sell for as much as a real fastback, but you probably aren't too concerned with resale value, are you? One last thought, a freind of mine desperately wanted a fastback years ago when he was in high school, but even then they were hard to come by and expensive. So he and his Dad bought two scrap fastbacks, one was a big block car with severly trashed shock towers and one was a race car project that someone had hacked out the rear wheel and fender wells, and grafted the two together. They cut them across the windshield and cut the floor across under the front seats, carefully welded them together and made one good car. He still owns the car today, and I've ridden in it and can attest to how nice the car really is. The doors close nicely and the windshield does not leak, which is more than I can say for some undamaged cars! Good luck!