GM didn't produce a dual wheel pickup with a regular type bed until the '73 model. Anything earlier will either be a cab/flat face cowl/cowl windsheild and chassis or a stake/flat bed. They also would have been made in the longer wheelbases on 3/4 or 1 ton chassis. I have heard of some GMCs that are made off the 1/2 ton short wheelbase with the 1 ton running gear, and even 4x4 versions, but have never seen one.
Anything that you might see in a pre '73 is going to be an aftermarket conversion. There's several on the market. JCW still markets them.
