Jay I done this in my 2 car garage with just basic skills. There are different ways. I'll tell you how I did it all by myself. I had a rusted out 67 fb that I bought to use as parts when I had the wreck. The top was good so I cut it off at the front pillars, removed the rear door lock panel and cut the rear quarters about 6 inches down from the crease at top and drilled out all spot welds for the quarter panel at back. Fastback corners at the rear panel are needed. There are some braces inside that also need to be removed. Anyway I got the top off from front pillars to trunk with all interior brackets. I brought it with me to fl. So while the engine was down I put the car on jack stands and leveled on one side of the garage. I installed 4 screw in hooks on the ceiling sqare above the top of the coupe. I got 4 small ratchet straps with hooks and connected them between the roof and the ceiling hooks. NOTE...My car is back halved with a 12 Point roll cage. It's not going to twist when I cut off the roof and I square measure the chassis and dropped plumb Bob markings for reference later. Ok, I hooked the top to the ceiling and cut the top off the coupe after taking a lot of measurements at the font window back of door pillar, quarter panels and rear end cap, always leaving more material than needed. BTW, you will need fb end caps.
I got the coupe top down and raised the fb top up trimmed the front pillars to dimensions taken earlier and insted of replacing the complete door lock panel I trimmed the fastback panel so it fit into the coupe glass notch and down the quarter over the coupe panel and preposition the panels at the cap ends. Take measurements before cutting then trim excess metal until I mock it up like I want it. I flange the fb qtr panel so that the coupe panel layed into the flange. Then it's a matter of tweek and stitch with the mig. I had to remove most of the interior brackets because of the aluminum interior and tubs. After it's all welded up, comes the grinding and body work till, you know what I mean.