Try thinking of it this way: in 55' the standard shift cars came with 3:70 ratio. OD 3sp trannys were 4:11. And that was a car equiped with either the 123HP 6 cylinder or the fancy new 162HP V8. In 57' the standard rear became a 3:55 for a car w/o OD. The tire diameters were smaller then too than what most of us use today.
This was all figured out by qualified folks who did their homework. (on sliderules) I still use mine occasionally.
