[horsa]

Not really sure how to measure or even accurately describe that curve. It is very minor though. The removable curved fender bolts on top of the flat extensions over the tracks. But it drops down below the height where the two parts come together. Likely something to serve as a reinforcement since it amounts to about two thicknesses of the metal. The swoop up towards the center of the fenders is roughly 2-3 more thicknesses of the metal in height above the bolt together location. So the slight dip, followed by the upswing makes it seem so pronounced.

If you still have the left and right vertical metal sections on the hull that the fender bolts onto, that should serve as a guide. The bolt holes are uniform in spacing, along with how the fender seats on it.