I can conform that Chevrolet had that ratio in 1956. I was a GM Tech and all I recall were 3:55 and up to 4:11 with a special order 4"56 ratio. In '58 I stared seeing a few 3:42's and then in '60 a few 3:08's. I'm using 3:08's right now in a T-5 setup behind a really warmed up 216 inline six and am happy with the outcome. I use a 30" high tire.