Several folks have done the 617 247 swap with success.

Myself, I have a 123 with a 300d na euro motor running a 307 diff and the five speed overdrive which about equals a 247 final drive ratio. Its very fine on the highway and the only real drawback is getting it going, especially if starting off on a steep hill.

And I have gotten as high as 36 mpg highway with it.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.