When I look at the photo of the bike Rick got in Ohio, which we think is a '54, I notice that the sides of the plate are curved (sort of a hourglass shape). When I look at the photo of Bill Marcum's bike, which we think is a '55, it has a mounting plate with straight sides (like my bike does, which we think is a '56). Does this give us the clue that '55 was the year they changed?
When I was cleaning up mine, I can see the impression of the curve on one side. Makes me think that maybe the tool broke & they just cobbled it back together without the curved punches in the die.
Mike Sal