Most of the time when converting to rear discs you get rid of the parking brake.
For a trail use only parking brake you can install line locks.
The caddy caliper idea came about to try to keep the parking brake and have rear discs at the same time. I think you will find that most of the time the parking brake part never worked right or at all and most guys just spent a bunch of time and money for a worthless feture on their trucks.
If you search the garage section here you will find countless posts on the Caddy calipers, parking brakes and line locks.