I used a photograph of a 2010 GT as an underlay and the only thing I changed is the c-pillar and lowered it. Other than that it's all ford. Even the wheels are designed after the old shelby 10 spokes.
Don't stare right at the part that changed and look at the whole car. Of course it is going to resemble something else, not like has never happened before. If you look right at the c-pillar yes it looks like a camaro c-pillar, otherwise when you look at the whole car, what does it look like?
Constructive criticism--If you're going after a first generation Mustang coupe look, I think it would carry through a little more as a Mustang if you didn't round the transition from roof to back window so much. A little more of an angle instead of a curve.
My 3 cents (trying to do my part to stimulate the economy).
Nice artwork! The "c" pillar makes it looks Camaro-ish. Maybe more of a sharp edge on the top side of the "c" like the old 'stangs had, then call it a coupe.
wow, thanks for the comments, I might dig out the file and do another version, I like the idea to make more of an angle which can still be done while rounding the rear glass. Most people might be suggesting the same, but it sounds like they are asking for a flat rear window, which would not look right on the car at all.