Nope . . the 2.45:1 came on the highway package in 70 on the B bodies. I had 2.45s in my 74 duster360 . . . it has the original e58 360 4bbl and 727 auto ... 235/60/14 tires, running at 70mph, rpm is 2600rpm . . . got 22mpg all day long !!! I know, not a b body or 383, but should be in the ball park ... . .