If you're willing to go without IRS then an inexpensive alternative is a Ford Explorer 8.8" rear end. Here's a comprehensive article on how to shorten one. The article has four parts. I've posted the link to Part 1. At the end of Part 1 you'll find the links to Parts 2, 3, and 4.
http://thefabricatorseries.com/build...prelude-and-qa