Since you are talking to Cass anyways, I would talk to him about the studs. Assuming I am correct in remembering that you are running his front kit. Did you end up with a spacer on the hub?
Probably worth bring this up even if they aren't using his front brakes. Maybe he can make sure the rear ones don't have the same issue, unless you have already confirmed it isn't a problem.
Yeah i have his 13" cobra front kit. No spacer used on the front or back. The rears mount great still but that might be because they're on the torq thrust II's which have a thinner wheel mount thickness than the mustang OE wheels.