All I would suggest to people doing this is try to stay at least 1/4" from the edge to prevent cracking.
Why not upgrade to vented rotors? I have stock vented rotors up from and 200mm drums out back, the mk1 stops on a dime even from speeds over 120km/h
As cool as that is, you are still nuts not to just put good vented rotors on it and good pads.