Mine is a GMC 250 with a flatbed, should be the same dimensions back of the cab. From the back of the cab to the rear of the frame is 96 1/4". I made a bumper/bar that extends from the back of the frame another 9". The flatbed is 102 3/8" overall and there is a 2 7/8" space between the cab and front of the bed. I also have a GMC 250 panel, it has factory extentions at the rear of the frame that extend it 12", the extensions are 'C' channel that bolt inside of the frame members making the overall distance from the back of the "cab" 108 1/4". These dimensions make sense, usually the 1 tons had a 9' (108")pickup bed. Both of my trucks use the same frame, just different mounts for the cab and body. I hope that helps.
http://community.webshots.com/user/0L50GMC
