The GM Media Archive has access to build sheet information for 1977 thru 2003 vehicles. I got a line on them from the Auto Restorer Newsletter. I think they charge $50 per hour for reseaching this info.

They can be reached at
gmma.research@gm.com

If anyone out there is successful with getting a build sheet from them, please let me know.

They finally acknowledge this information does exist. Of course, "for a fee"...