It can only be done if you have access to the correct machinery, specifically a CNC vertical mill, or a mill with a rotary table. NOT A DRILL PRESS. The setup is involved and it is very time consuming. The opportunity for error is great and the ultimate result is the compromise in strength & reliability (IE:safety) of the finished. To do this correctly (holes) there is a formula that takes into account the thickness of the rotor, the width of the friction area vs the diameter of the holes used on a specific rotor. (how much material is removed). I chose to do slots in mine.
Attached is a picture of the rotors that I modified by the above process. Each rotor took about hour once the setup was done.
http://www.clubcobra.com/photopost/s...t=1&thecat=500
Rick