Hello everyone,I have a 1974 Dodge D100 318 3 speed manual shift truck.i would like to install an overdrive trans to improve fuel mileage.Is there a transmission that would fit my bellhousing etc and be a fairly simple changover?The transmission I have now is a fully syncronized 3 speed side loader and the differential ratio is presently 3.55 Thanks for any replies and also thanks for any other fuel mileage tips.