This is an interesting topic, as it challenges us, decades post the original production to attempt to determine the intent for a component modification by Ford.
First I assume that no one here apparently is either a first hand witness, nor holds any documentation or is aware that any currently exists describing the reasoning, so we are all speculating?
If so, I am a little at a loss to actually believe that the real engineers at Ford, after concluding that there was interference between the damper's' outer diameter and the sway bar would choose to bevel the edges of the damper solely as to avoid a perhaps more aggressive notch from being formed from the corner edge of the damper into the sway bar, but still permitting this interference otherwise? If one considers the impact (pun intended) of this event upon the components directly involved, and the resultant effect upon others even if only indirectly, then I say: no way!
As far as a secondary bevel to the rear of the inertia ring perhaps for the purpose of balance, I don't feel there is any credence in this, as a symmetrical material removal at the face would not cause a change or imbalance of the component (as relevant here), therefor a like removal at the rear has no purpose in this arena. But what is accomplished, and I believe the intention, in the change (reduction in this case) of the inertia ring mass is a change of the harmonic vibration dampening effect, or "tuning" of the damper for the 428 P.I. engine requirements versus the 427 application from which the dampers' engineering originated, and such a change otherwise I believe would not have been approved by those responsible for such, with other simpler solutions for chassis fitment purposes available.
The sway bar spacers and change of the profile of the bar both appear to be a response to the apparently overlooked issue of the interference, and it is feasibly reasonable to me to believe that this issue was just that, and that the dampers' profile change had nothing to do, nor was intended to address this interference, as it was ineffectual for such.
Well, I wasn't there, and my ears are not deaf to other's, but that's my speculation on the matter, for whatever it may be worth.
Scott.