All of the Vintage Air manuals are available on their website. There are multiple options depending on whether your truck had factory air, or not, and whether you want to use the factory style AC controls or not.
Here is the link to Vintage Air's installation manuals page:
Vintage Air GM SureFit Instructions
Browse down to the
"1967-72 Chevrolet/GMC Pickup (also Blazer and Suburban) (Gen IV Electronic Unit) Factory Non-Air Vehicle Only"
or
"1967-72 Chevrolet/GMC Pickup (also Blazer and Suburban) (Gen IV Electronic Unit) Factory Air Vehicle Only"
section as appropriate