Re: Rear suspension?
Just remember this thought....
A poorly configured (geometry wise) 4 link or 3 link or ladder bar setup will ride and drive worse than a leaf spring setup. The factory GM leaf spring setup is simple, reasonably well designed, and does the job asked of it pretty well. (that goes for a lot of other things too....)
If you go building a 4 link setup, you'll have alot of things to consider, like anti-squat, instant center, roll center, center of gravity, and the like. You'll need to figure out where to put the instant center, what link lengths, pickup points and angles work best for your truck and put the instant center where you wanted it, and so-on....Not to mention figuring out how to avoid significant roll oversteer or understeer, what type of centering device you want to use (watts link, panhard bar, angled 4 link, etc.) and the multitude of other choices involved.
And if you're going to do all that, you probably shouldn't use the factory 7.5" rear. You should consider a 8.5" 10-bolt, or a 12-bolt, or a 9" Ford, or a Dana 60 (which is a beast, but also nearly bulletproof in an on-road truck).
I think Air Ride Technologies has a bolt in air bag system for the rear. You might check them out and see....
'JustDreamin'