How bad are they hitting the caliper? If it's "just a little", break out the die grinder and add a little clearance. (to the calipers) If it's a lot, then add enough spacers that "clearancing" the calipers and adding the spacer solve the problem. (That way you use the thinnest spacer possible.) The rule of thumb for wheel stud engagement is you'll need to have at least as much of the stud in the nut as the stud is wide. (You need 1/2" engagement on a 1/2" stud...minimum.)