Excellent point,
I also didn't notice any grinding marks and I wondered about that as well.

But,
I also noticed the restamps were done from a lower, right angle, implying (to me) the restrikes were done while the trans was in a vehicle and may explain also, why the stamps for the OB2 are so butchered.

As far as a dealer, why would they change the numbers, there's no doubt or question that #'s were changed.

Seems like there's more reason to doubt its authenticity than prove it ?????
Or are the above mentioned reasons enough to unequivocally prove its authenticity?