Visually I see 2 maybe 3" MAX in the video. They did state that GM used the position of the axle on the springs and the shackles as their reasoning for the change..
Which goes along with my theory...
Makes no difference though. We already KNOW what the result is due to the CAT scale tickets.
100#, so do some backward computations until you arrive at a method that matches the result.
That will be the correct method.
As an aside, banter on GM forums is that this move was only for the SB/CC models.
It kind of makes sense, as that configuration could benefit from such a change.