In an effort to simplify the large-scale assembly process, the Gen III V-8 uses torque-to-yield head bolts. This means the bolts actually stretch beyond their reusable limit, or to their plastic yield, to provide a consistent clamping load on the cylinder heads. Notice the different lengths: The head bolts look like this for engines built from 1997 to December 2003. After that, the bolt lengths were standardized to the 55mm shorter versions in January 2004.
Gen III GM Small Block Tech