All you really need is the 3rd member from the rear axle. They're pretty prevalent in junk yards at this point.
Key thing will be gear ratio. The 1st gen was available in 4.63 & 4.90 gear ratios. If you look at your door tag, at the bottom there is a section for AXLE. Underneath that it says HG46 or HG49 for the 4.63s or 4.90s respectively.
So just make sure your donor truck has the same gear ratio. Look at the back of the axle housing, if it has an LSD there will be an orange sticker on the back that reads "LSD OIL ONLY"
Provided you can find one with the same gear ratio, it's a bolt in affair. Depending on the mileage the LSD could do for a rebuild. Which is not that hard, but takes a press to get the carrier out of the 3rd member.