The frame on a 1/2-ton (GMC unique 100 model/long-frame, see picture of one I parted) This truck is simply an extended 1/2-ton truck with 1/2-ton suspension pieces.
http://good-times.webshots.com/photo/2967102110102454676BWyNDC
This frame is going to be 46-1/32" wide at the rear. a 1949 3/4-ton frame at the same location is 36" big difference. It is in the rear where the major differences occur due to the heavier rear differential and spring set-up.