If your truck was built in Canada, or built in the US for Canadian usage then you may be able to get the information from Vintage Vehicle Services through GM of Canada (George Zapora).
Send them $60 and your VIN and they will send you the original RPO content for your specific vehicle (if they have it).
Link:
http://www.vintagevehicleservices.com/gen-tech.html
The US counterpart, the GM Heritage Center Archives, does not have information prior to 1976. If they had it they would be able to provide the original invoice, which includes option content and pricing.
Once you have that info, forum member Chipflyer can make you a new SPID label.
K