283, 327,350 it really doesn't matter. A good rebuild with quality parts. It can be done with carberation or fuel injection. Just a good tune to a good engine. Gearing needs to be high enough to let the engine loaf along (within reason)and for most drivers the automatic transmission will yield the best results. It takes a skilled driver to work the stick shift tranny to its optimim. If you have it put together right and you drive like you have a raw egg under the accelerator most anyone can get the magic 20mpg. Not much science to it just good ole common sense.
