If I recall the cobra wheels have even more backspace than the standard 17" wheels so Id have to say no they wont work. If they have the std late model backspace they will work with spacers,. the thickness you need varys. I needed 1/2" in front, some need 1". The rears will need 1" unless you go the route I did. I added a 9" rear from a 67 thats 1 inch wider on each side. HERE is a pick of mine with 2001 17" GT wheels.
that 65 looks KILLER with those wheels on it. I'd thought about using those wheels but wasnt sure about how they'd look, but i really like it now. the price is always right on those too cause most late GT's have them and a lot of guys are upgrading. now if only i had some of that weird green paper stuff...
I have some real '95 R's that was going to go on my '65 fastback. The backspacing on the real R's is 5.95 I believe. Theres really no easy way to make them fit on a 65-66. If you space the front out they wont fit inside the wheelwell. The back actually will fit with a fair amount of clearance. We discovered that if you have about an inch taken out of the middle they will fit perfectly, clears everything and perfect backspacing. Although they do look awesome, it was just to expensive to make them work. Here are some pictures we took while we were mocking them up. Sorry about he quality, it was a polariod that was scanned-no digital at the time.