Usually we will run a 7" bag. We sell the Porterbuilt kit, which uses the 7" SS7 Slam bag, and works well in this application. You could go with a kit like mentioned, which will come with the shocks, bags, shock brackets & bag brackets. It is recommended to do a adjustable trac bar to help center the rear end and allow less movement through the suspension cycle. A c-notch will also get you a little lower as well.
The Stage 1 is bgas, shocks, and brackets.
Stage 2 is the same, but adding new shocks bars for upper and lower mounts, adjustable trac bar, and c-notch.
Porterbuilt Stage 1
Porterbuilt Stage 2 Basic