Unlike the modern trucks of today, crew cab trucks from the 70's & 80's were considered work trucks and heavily used by governments and utility fleets. Many were 4wd, some were 2wd, but back then they were all at least a 3/4 heavy duty chassis. This being your build, it would and could be possible that some creative type builder went the lowered half ton route as well. Will be interesting to see this one when it's done, you are off to a nice start!