[LONGHAIR]

3" is pretty much the standard for bodylift kits. On these older trucks the kit is pretty much just the blocks themselves along with new bolts for the cab, along with carriage bolts w/nuts for the bed. The hardware pack also contains an "extension rod". It is a simple 3" long piece of steel rod, about 5/16" or so. It works for both automatics or manuals. You simply saw the clutch rod that goes between the pedal and the bell-crank on the frame and weld the extension in the middle. (Same thing with the shift linkage in automatics).
I always did it by clamping all three pieces to a length of angle iron. This keeps them straight and makes it easier to keep the ends aligned. A couple of tacks and then remove it to fully weld the rod.
The only other thing in most of the kits is a short piece of tubing that is used to extend the fuel filler hose. A razorknife through the hose and a couple of clamps and that is done.
The brakelines, wiring and other connections from the body to the frame will have enough slack.
The only other consideration is the fan shroud. Some of the early trucks just had a glorified hand guard, the later ones get more involved. The "kits" instructions usually tell you to just remove the lower half......not the best idea. It can get you into overheating problems. A little fabrication goes a long way here.