Have you looked at any of the links I posted? Centric calipers are listed with the spring and bracket. The park brake is built into the caliper so there are no separate shoes. They have several different styles of rotors and pads so you can choose a combination you like. Centric also has a very good tech line. I've used them for a number of issues. They're honest imo. I have been told "Our products won't do what you want" which is very rare to hear these days.
King caliper is a rebuilder close to me. I source King parts for many of our fleet vehicles. I have spoken directly with the engineers there for specific applications. I have sent calipers to them that they do not list in a catalog and they have rebuilt them and sent them back. Their web site isn't much to look at but their brake work is good.
http://www.kaliper.com/
IIRC (it's been many years since I went down this road) Cadillac switched some models to metric fasteners in the caliper while Pontiac, Buick, and Olds took longer. So the bleeder and the banjo bolt were metric in some but not all. You could bolt one caliper in place of the other but you'd have to source a new banjo bolt.
FWIW I would not attempt to put larger rear brakes on a TF truck without the truck having a better weight balance. The front axle carries a much higher percentage of the weight than the rear and putting in highly effective rear brakes can increase the tendency for the rear wheels to skid in a stop. This is bad. Locked rears turn your pickup into a top ready to spin at a time when you need directional stability.