I agree with your comments and suspect the modification MIGHT
only apply to a current model i.e. 2008/9/10/11 up that has not changed since the last major refresh. I do not think that you could simply install a shield on a older model with lighter axles and/or the 4spd transmission etc.
From what I can tell from looking at Ford's published information at https://www.fleet.ford.com/truckbbas/
(Body Builders Advisory Service)
the 2010 (which I have) and 2011 are nearly if not identical in every way so this in fact MAY
be all there is to it on the current generation chassis.
I leave it to each owner to make their own call.