I recently completed refreshing the rear disk brakes on my '89 Formula 350. The rear rotors are the original GM part. I had them turned and reinstalled them. Noteworthy here is the close fit of the stud holes in the rotors around the studs in the hub. Moving on to my question.... I recently purchased a '96 Z-28. I removed the rear wheels yesterday so that I can redo the rear brakes on this car as well. Noteworthy on this car is the LARGE hole size in the rotor relative to the stud size. They fit snugly around the center hub so there isn't a problem with centering. I can find no evidence of a GM casting mark on these rotors and am wondering, "Is this right?"

Is it normal on the newer ABS cars to have the large holes for the wheel studs in the rotors OR did somebody do a sh*tty brake job on this car prior to it arriving at my place?

I appreciate any guidance you guys can offer. Thanks - Keith