With the studs made you simply thread them into the backing block. If you got a little aggressive with the tap it's not the end of the world. Mix up some slightly thickened epoxy and apply with a syringe into the hole, wax the stud and thread it in with the thickened epoxy and let it cure. This will create a nearly perfect thread interface between the stud and backing plate. Even with a good tap I still dip the stud into epoxy, coat the inside of the hole and thread it in.