should not be done but I would assume the guy that is going to do it is a bored body/paint guy that happens to have a good hard top and a totaled convertible sitting and gets a crazy idea after drinking a 12 pack and cut up both cars before he sobered up and decided not too. He woke up that next morning, saw the cars all cut up and though, "WTF was I thinking?! Oh well can't stop now...." By the time you figure in the price of a clip, the time to get the quarter off of your car, time to get it off the parts car, and THEN you start putting them together. Just when your really starting to have fun you get to start the body work and don't forget you will need to figure something out for what to do the the roof line both to just seal it from rain as well as not look stupid.... No use in blending 2/3 of the car back to the othe 1/3 so you better go paint it all and then you will have someone occasionally go crazy if they notice it. Does all this sound like its worth the price paid in $$$ and time?
If its really that important to you, it would be cheaper and even easier to find an original cobra with the hard top vert option and it will also be worth 10X then the modified version when you go to resell it.