To use a '03/'04 Cobra hood on a GT,all you need to do is drill two new holes behind the factory holes were the GT's facia mounts on the headlight/bumper cover bezel(the fiberglass support),right at the top.You can't miss them.The top off the facia is held in place with two plastic type push in plugs that look like screws.Bring them closer to the rad support to line up with the Cobra hood.
I've seen this done,and looks sweet.Just take your time,and don't rush it.You would only have one shot,unless you refiberglass the holes over
.All depends on how picky you are with your car,that itself shows the workmanship in detail.
I've also seen the '03/'04 Cobra facia on a GT with stock GT hood,lined up perfect,but that is another story
.