The steering boxes changed during '56.
'55/'56 steering boxes are Two tooth, the '56/'57 steering boxes are Three tooth. With a bit more surface area on the gears the Three tooth version generally holds up a little better.
(only one of the first three images is a 50's Ford part, the other two are just visual aids)
Photos 4 and 5 are top views of: '55/'56 and '56/'57.