I don’t know what the factory’s intent was, but it would definitely make more sense if the rib squarely contacted the stop. The fact that it contacts the stops at an angle means that any slight variation in the location of the FT124 (up or down) would allow a greater change in travel. Given the machining tolerances of the day... that could mean you and I were lucky and Master Phelps not so much. Is there something else coming into play that caused him to have a string of bad luck? At the end of the day, it seems (at least in my photo above) that the FT124 hits the headstock before the rib can get square against the stops. Other than rather random tolerances etc the only other variable (based on info provided in posts 1,3) would be the lower bearing. As in were the bearings replaced? What were the dimensions of the replacement bearings versus the originals. Not just the width of the outer, but the total width including outer, balls, and inner. Perhaps the business part of the race wasn’t ground as deep? Again.. given the rib contacting at an angle, it would not take much to allow more travel.
Does the spares co. have any drawings that would show the dimensions of an assembled bearing?