Parnelli,

In regard to your question if you look at the T&C rules Group 3 and Group 4 is for saloons or sports/GT cars from 31 December 1977 to upto 15 years old.

Then if you then look at the brakes the only permitted mods are friction materials ie pads etc. Rotors and calipers can't be changed from the oem items or oem spec items. Eg wilwoods are aftermarket caliper so not oem so can't be used on a post 77 T&C compliant car.