Basically, all you'll be able to use from the 03 Cobra is the brakes (rotors and calipers). The rest of it won't work. You need spindles off a 94-95. 96-98 spindles will also work if you are only going to be running 8" wide wheels. I believe there are clearance issues if you go any larger.
Also, the struts may or may not work. I'm not 100% sure on that one. I think I've read that they will though.
I've got 255s on a 9" wheel on mine. They rub at full lock, but it's not too bad. You could probably put 275s on there and sacrifice a little more turning radius. Mike (Silverstangboy) had some on his car for a while.