Truely "stock" "as built" trucks are rare here. Most people have done small changes to their trucks. Even something as common as a wheel change or substitution of an obsolete tire size can change the perceived appearance.
Since you have only narrowed it down to twenty four different models/years being more specific would help.
Probably the best place to look is at factory literature and advertising.
Start at "The Old Car Manual Project"
http://www.oldcarbrochures.org/NA/GM...rucks_and_Vans
Look through their specific brochures and see what you like. Then a search through eBay at brochures and ads will yield a lot of pictures, as many sellers post large, useful picture of period stock trucks.