Carrera, do you have TT arms and/or S3 spindles ? If yes, they can't possibly fit as they've been designed for the standard GTI arms & spindles (although I can't imagine them using these heavy iron parts on their racing cars). There would be 2 problems :
1) S3/R32 brakes do fit both GTI & S3 spindle because the caliper bracket mounts on the outside face of the spindle wich has the same distance related to the disc mounting point on the hub (wheel bearing). However, as the aftermarket caliper brackets mount on the inside face of the spindle, the S3 spindle is 16mm thicker than GTI one (33m for S3 and 17mm for GTI) wich means new brackets (16mm elongated) need to be made. Dave is doing these for my Ap Racing brakes as we speak !
2) The tt arms and ball joints will also interfere with the lower side of the brackets so they need to be modified there also