That engine alone is a big enough difference in itself. Almost nothing at all inside the block is interchangeable, and is built to last longer. There's lots of other little detail stuff as well, such as seat material and stitching (mentioned in the Jim Carter catalogue). I've been digging for a year or so to track down every difference between the two. It's interesting, and sometimes very frustrating, when you own one and need certain parts.
This page at oldgmctrucks.com states most of the bigs differences:
http://www.oldgmctrucks.com/page0375.html
