Here are a few pictures of the rib in question.
There is obviously a separate section of rib that runs maybe 1.5" from the rear of the barrel
assembly to about the back of the 0 on the 20 engraved designation.
The rear sight is maybe 7.2" forward of that and is obviously dovetailed into that section of rib.
Based upon the rear sight I'm thinking the rib between it and the breech is pretty robust.
However, when ever I see pivot mounts atop this gun there seems to be a reinforcement
(that the front pivot base gets dovetailed into) applied to the area of the front mount?