Spec quality is hit or miss. Our Spec 2 in the 2001 GT went into the trash early. Replaced with a King Cobra and have been quite happy. For your 03 though, you have an 11" clutch and the KC is 10.5". You can do the 10.5", but you'll need to swap more than just the clutch kit.
I'd check into the Centerforce Dual Friction kit...I have not heard one bad thing about this clutch.
Also, you could look at McLeod. White Stang, did you see his sig? He is definately NOT stock...