[dsraven]

my sugestion
get the body off
strip the frame with pressure washer or whatever to get the lumps off
get it on stands and level it up quick
check for rusted out spots or thin spots in the frame around connections where shock mounts rivet on, cross members attach etc
with a tape measure and some mask tape mark each cross member at it's center point from side to side
take a string line or laser and run it from the rear cross member mark across to the front cross member mark. see if all the marks in between line up
now check from corner to corner dimensions to ensure it is square within 1/8". have a helper or vice grip the tape to the frame so you know the tape is in the same spot on each side
now check it for sag with the string line or laser
now look for loose rivets, cracked cross members, cracks in the main frame etc
if all good decide what you will want for an end result as far as suspension goes. what will be the purpose for the truck, eg, canyon carver, straight line racer, grocery getter, weekend road tripper, in the weeds, only slightly lower than stock, adjustable air ride etc etc etc. that will help you decide what your underpinnings will be. then decide what your power will be and that should help you decide what your rear axle will need to be and what frame mods will be required. remember that these trucks are not very heavy so they get squirrelly with big power. if you plan to lop off the front and weld in a clip from another car, then lop off the back and weld in a C notch, then you might as well do a new frame or a swap frame because the only stock part of the frame will be the part under the cab
what do you have for skills, tools, shop to work in, storage area to keep all the parts in-you will be surprised how much of a pile there cab be. what will the budget be, account for over runs and the slippery slope of "while I'm here I might as well do this too". that should help you decide how far into the pocket book you can reach for parts. strip your parts down so you know what you are looking at for stuff you will need to buy. take pics as you go and sort of re-assemble stuff when you take it apart and box it up so you know what bolts went where and how. I suggest to buy a donor vehicle if you are on a tight budget. something with the engine and trans you would like to have. that way you get all the peripheral stuff. insurance write off auctions can be a place to start.
let us know your intentions