This thread may prove helpful. Post #4 shows the area that normally causes interference between the disc brake caliper and the backside of the stock rim. Sometimes the interference is so minor, a small amount of grinding on the caliper can solve the problem, or a 1/8” or ¼” spacer between the wheel and the rotor may also solve the problem. If this is a desirable option, you just need to make sure the studs are long enough to provide full engagement with the lug nuts.

http://67-72chevytrucks.com/vboard/showthread.php?t=430426&highlight=disc+brake+wheels

1960 GMC 1/2-Ton Pickup Truck
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