A little help with brake drum measurement please
 

I am about to order my rear disk brakes and I have a question for the C10 2WD guys. I have a six lug axle and I want to know if I will need to machine my axle to fit the new disks. What size is the hole in your drum? Mine measures 3-9/16" across the large hole in the center of the drum. ( I believe that is referred to as the register) If you can tell me what yours measures that would be great!