D4/5/600 Crew Cab

Thinking about building one. Found a decent "first gen" crew cab, which seems to be the more difficult part of the equation lately, and if I can get it cheap enough I will find the medium duty to mount it to later. Anyone here build/know of any big crew cab trucks running around? Pix and links would be nice.

This generation of Cab? or this one



I have a crew and a truck for the second generation. Just trying to figure out how I can get a cummins in it and travel at more then 40mph. I want to build it for towing my mud trucks

"First Gen"

Second photo.