I put a 1969 roof on a 1987 targa. This was the only time I have ever done anything like this. Here's some issues I had to work through:
I made metal jigs for the front windshield, back windshield, and rear quarter glass to make sure the glass openings were close enough.
The A pillars were different widths, and I didn't fix them - so you can see the change in thickness from the inside of the car. I added a metal spline into the pillars to add some strength.
Try to get the headliner rods with the roof, because they seem to vary.
I had a heck of a time getting the roof to the back of the C pillars correct.
The interior trim for coupes is different from the targa so I had to custom make the rear quarter window interior trim.
I don't regret it, and it turned out better than I expected, but it was a lot more work than I expected.
Mike