getting + miles a gallon by changing gears in car?

[HotRod58er]

i read a story about a guy way back who modifiend his Chevy Nova and put very tall gears in the transmission and very small gears in the rear end and went from Miami to Los Angeles at 80 miles a gallon! Now About our Buicks. Since I have the sycromesh shift trans and economy rear end gears, I thought I would ask. What is the tallest gears you can stick in the transmission and the smallest rear end gear you can stick in the rear end of a 58-59 Buick?

Thanks
Josh

[Resurrector]

Wow, I don't know if you could improve on what you have for gears already...I get what you are saying, interesting thought but as far as that story, it's a load of crap, keep in mind that- for example- a subcompact Geo Metro, with a fuel injected 3 cylinder and a 5 speed, driven with an egg under the gas pedal, can barely squeeze out 50 mpg in the real world, and it's much lighter and FAR more aerodynamic than a Nova!!

I used to get caught up in trying to improve mileage of a 2 + ton American classic, but ultimately realized that unless you are using the car every day, the difference between 17 and 24 mpg will not put you into the poorhouse
Once I put a Buick 3.8 V6 into my D100 pickup, in the hopes of improving mileage, only to find out it gets no better economy than a V8, just has to work harder and has less power!
Lesson learned...my two cents!