I would look for another car without so much work lol But, If I had to pick a car out of those two, it would be the C code only because you don't need to replace the roof. If you are going to fake a GT, then you can do that with either an A or C code, although GT were only made with A code and K code cars. A car made into a GT regardless of the code is still a fake one if it was not ordered that way from the factory, so it doesn't matter.
65 k code fastback
67 SS Camaro convertible