The lengths are indeed different.
The 3/4 and 1 ton frames differ from the 1/2 from the back of the cab to the rear stubs. They do not flare out to the sides. The run straight back parallel to each other. The 3/4 &1 and 1 tons also do not have the 'kick' up over the rear axle.
From the cab forward, I believe they are the exact same (frame wise). The have different springs and mounts but the frame rails are the same I believe.
If I'm wrong Bolters please correct me.
I'd check before you buy an IFS JUST TO BE SURE.
