unless i'm mistaken that part # is for an 8 rib belt, so you might have a problem. i think thats a gatorback #. autozone or most local auto parts stores should carry it. you can also by from autozone.com
Call me stupid but dont all 03 04 Cobras have 8 rib setup?? What type of setup do you have? I see a 2.8 upper and 2lb lower, but what else?? Aftermarket idlers or stock?? The last numbers in the belt are the size in inches. That is a 77.2 inch belt that you are looking for correct? The 77.4 will be easier to find and should work correctly. Maybe this will help http://www.stangshiftergaskets.com/belt_selection_guide.htm
Scroll down until you find your closest setup.