Here's a little info on springs for these Chevy's.
There are 2 different size rear springs, 52" and 56". No one, including GM, seems to know why they are on some trucks and not others. Front springs were all 48" (some say 47" but they are all the same). You can take the rear 52" springs and put them in front, remove the overloads and you will get around 4" lift and a better ride, but it requires a lot of work. Putting 56" springs is also doable. Then you just need to buy springs for the rear. If you are buying a lift make sure you measure your rear springs along the arch from eye to eye, not straight across.
Another thing you can do for the best leaf spring ride possible is get the rear springs from an '88-'98 truck. They are 64", though you need to move both your rear spring hangars to do this but the ride is Cadillac comfy!
Also don't forget if you lift your truck you will need longer brake lines, longer shocks, lifted steering arm, longer driveshafts and if you keep the sway bar you need extended links.
I think that about covers it.