The dimension I guess would be from the front of frame rails to the back of cab for the pre 98 std cabs versus the extended cabs. The difference is what im after between the 2 measurements. Im thinking of getting a extended cab roof line & extended cab rear section from a truck off of C/L. I would be cutting the A-pillars about 4" below top of windshield & the floor about 12" forward of the back of the door opening. When I get the cab section I would also cut a section of frame from each frame rail,but unsure of how much the extended cab is over the std cab. I'm thinking that a 3' section from each rail should be enough & then I would buy new C channel to reinforce the frame in the area being spliced.