In the past I would cut off the stock studs of an early (71/73) Pinto rotor and drill new holes for longer studs before they showed up in speed shops. All I used was a mill, but you could use a drill press if you took care. Doing this on a 9" rotor should be no harder than on a 10 or 11 rotor. You might have to plug one of the old holes but there again, no big deal. Would it be true? Try checking a new 9" Pinto rotor and you will see how far from true they are after they get here from China. All that stuff is mass produced and as such, it has a + or - tolerance. I've done this for years with out a single problem. This way you could have a big rotor and 4 lugs too.