Lovely pictures, Statik, an easy thousand words in each.
Given that it's taken 60 years of use to get to this stage, you could fairly confidently rebuild in the same gauge, but I'd look at putting a plate across the underneath, taking back either side of the rib. Sure, this will take up some of the pre-load in the spring, but that's all it will do. Hypothetically this will change the geometry, negligibly, but not in practice. In practice the whole thing is completely dynamic at all times, and even a quarter inch would be negligible; and you can bet that over its 60 years the spring has sagged more than that anyway. To properly change the geometry you need to start messing with link lengths, and that's not happening.
Ahhh, Statik, I see you went to "one of those" schools.....
JFerg