HiPo shop has many, many threads debating the different options...in a nutshell, here's the players-Mustang II, Camaro/Firebird/mid-size GM clip, or AMC Pacer. The Pacer allows a stock ride height(not lowered) and replacement parts are HARD to find. The front clip off of Camaro, Monte Carlo, et al offers full replacement parts coverage, but may have too wide of a track for your truck, plus you have to cut off the front 1/3rd of your chassis. This leads us to the Mustang II. VERY popular swap, all kinds of replacement and upgrade parts are available, and kit crossmembers requiring almost no frame cutting are fairly reasonable. If you can weld with a MIG, or have an acquaintance who can, then this is a no brainer. Save up for the Mustang. It will be worth it.
Wannabe
P.S. Go to the Gallery and check out ChuckTheTruck's website link. His pictures do a pretty good job of illustrating how relatively easy the Mustang II is to install