Here is a couple options you can try:
First look under the seat between the springs and the pad on the seat bottom or on the back side of the seat back, most of the time thats where they were put on trucks. You may just find the orignal build sheet there.
Second try GM you can get a restoration pack by calling GM Customer Service at 1-800-222-1020,
you will need the following information when you call, year of truck, Vin # and Model they may also be able to provide a build sheet for your year.
