The 'bolts' are really pins with a thread just under the head. Regular gm stuff. Not exactly the same but watch this from about 12 minutes and you'll see what you want to know. Chris
Pretty much a standard issue caliper bracket for a GM caliper that is used on an early spindle. The caliper slips down over the rotor and the bolt and pin as it is called goes through that hole and through the caliper Through the bracket and through the other side of the caliper and the threads screw into the threads on the bracket with the bushing being clamped tight to the bracket for the caliper to slide on. This is how single piston GM calipers work.