The crew cabs where custom made for the railroad and who wanted to have one built. if you google (1972 crew cab) you will find pictures of the originals cabs they look like 2 cabs welded together. there is a guy in Washington building crew cab with 4 doors they are pricy at $15,000.00 for a cab ready for primer. Check o0ut this thread
http://www.67-72chevytrucks.com/vboa...d.php?t=319781