When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
That is very similar to my plan. I have a Keisler RS500 Perfect Fit coming soon. In addition, I am going to convert to a hydraulic clutch so my wife can drive it too. Gas mileage will probably go up the more she drives it because her foot is much lighter than mine.
As has been previously mentioned, anything that will make a significant improvement in mileage will probably cost more than it's worth (trans, diff). The only thing you can do that's 'free' is to stick to the highways rather than stop and go driving.
Poor old '77 is getting about 6 mpg right now. As much as the t-tops have leaked over the years, I think I can kick the floor pans out with my bare feet and "Fred Flintstone" down the road. Stopping might be a little hard on my heels.....wait, it's a C3...I don't know what it's like to have brakes anyway!