I also got my new parking brake cable retainer from GMCPauls! It's the little things like this bracket that I lost that really make a big difference. I think I threw my original one away still clamped to the old cable....
I started by prying the clamp open to get it over the cable.
Then I took a pair of channel locks and slowly pinched it back down over the cable. Installed the bolt and pin.
Then I got back under truck and adjusted the double nuts on the parking brake cables and all done. Works like OE