Picked up this old tired '75 D100 for cheap with about a million miles on it....500,000mi actually.It started life as a heavy duty 1/2 ton D100 shortwide 225/6, 3 on the tree, 3.55 gear 9 1/4 rear and 11" brakes. It was from the Enid, Ok air force base and was sold to the Northwest Oklohoma State University, where it was swapped to a NP435. Trucks at the college aren't cared for very well and it was sold to a local who used it as his hunting and fishing rig. He then sold it to another guy 15 years ago and I got it last year. The first time I changed the oil was the first time it had been changed in 15 years!!! Says a lot for the good 'ol slant six, huh?