If you use 12"OD (or larger) brake rotors, be sure they will fit inside the wheels you have. Also note that running 12"OD rotors does nothing unless you also move the calipers outboard to take advantage of the larger OD rotors and their extra 'hydraulic leverage'. Otherwise, you're just carrying extra dead weight that's not being swept by the brake pads.
And speaking of weight, the Gr-4 race cars with their big brakes, flares and giant slicks weighed about 800 lbs less than a stock Pantera. They could have been even lighter but those were the FIA competition rules in the '70s. Doesn't matter on the street or in amateur competition, of course.