99-04 GT brakes are dual piston but not a bigger rotor like the Cobras. To do the front brakes you need the calipers and caliper brackets. And obviously rotors and pads.
For the rears the 99-04 GT is the same as any 94-98 GT. To upgrade to the Cobras you need to pull the axles, change the caliper bracket mount and then you re-use the calipers with Cobra caliper brackets and the correct Cobra rotors and thinner Cobra specific pads since the rotor is now vented and fatter.
It is a big difference, I would not waste my time with the 99-04 GT front brakes. The difference between the 94-98 GT and the 99-04 GT is marginal. Going to the full 94-04 Cobra/Bullitt/Mach setup is a very big difference in braking.
2000 Mustang GT Steeda build #48. Bolt ons, suspension, Novi 2000.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.