The GT500 rear brake upgrade is the simple and practical alternative. As I understand it, it is basically a bigger set of rotors and a bracket to move the calipers for the bigger rotors. The only minor complication is you have to remove the axles to mount the brackets.
This kit has the front and rear brakes but I'm pretty sure you can get the rears separately. http://www.americanmuscle.com/ford-r...rade-0514.html