I know this has been brought up before, but for the benefit of our new members to the Stovebolt, I thought it would be beneficial to bring it up again.
Chevrolet Motor Division has a FREE Restoration Packet available for most all trucks. You can call toll free to the Chevy Customer Assistance Center (1-800-222-1020) and request your free packet. You must have your VIN ready to give the clerk as the VIN will determine the Technical Data Sheets that will be sent to you. In addition, they will include a book on "Past Model Information" that gives a lot of sources for parts and information. Not a bad deal as even the shipping to you is FREE! (Mine was shipped UPS).
If you own a Canadian made GM truck, the Restoration Packs are available, but unfortunately, not free. The numbers to call for your packet (in Canada) is 1-888-467-6853 between 8 am - 5 pm Eastern Time, or (outside Canada) 1-905-644-3387 or 1-905-644-4060. You can view the contents of the packets by viewing the GM Canada site.