Posi-Traction and a Solid Axle are two different things. A "posi-track" is a traction device used in a "solid axle". A solid axle is what you have in the rear of your truck. According to your trucks former owner, it's a 14bolt. I'd assume (don't take my word on this though) and say it's a 14 bolt SF (Semi Float). The front axle will be the GM IFS 8.25.
You're rear axle is a solid rear axle. Front is IFS. Independent Front Suspension.
There are a few different types of "traction devices" used in solid axles. Just google some of them. Lockers, LSD's, Lockout's, Spools, Mini-Spools, Welded Differentials. Yada yada yada
Live-Axle aka Solid Axle
http://en.wikipedia.org/wiki/Live_axle
Do yourself a favor bud, start researching about your truck. Crawl under and take a look at everything. Understand what axles you have, and lift you have. Once you have a good/full understanding about your truck, then start deciding on what you want to do with it. And what/how you wanna build it.