The Blazer is shorter than the shortbed PU. It is much easier to convert a 4wd to a 2wd than to shorten a shortbed frame to fit. You can do a simple leaf flip like Soon mentioned or you can install trailing arms, but it takes a bit more fabrication.
Check out this article explaining how to do the conversion -
http://www.sporttruck.com/techarticl...ion/index.html