Are there any kits to convert a hardtop into a fastback from 64 1/2 to 68
 

kinda self-explanatory :)

Only way I know to do it would be to buy a donar car and swap it. If you're going to do it yourself....have lots of tools and be a very good body man. It is very difficult to do.

When I ran a body shop, we would have to put a roof on a vehicle every so often. Usually a very new vehicle that experienced a roll over or tree falling on it. You have to line up the windshield, rear glass, side glass [if it has it, or eleminate them] and match the door glass to the top. Real difficult.

Would be cheaper and easier to go buy a fastback.