V/8 Swap

A /6 to a V8 swap is worth it IMO.
If the /6 is worn out and/or your just not interested in rebuilding the /6, the V8 for mileage is a reasonable option so long as you don’t start in with adding a larger cam and gear and etc…..

Typical hot rod parts, a carful selection of a cam for mileage can go a long way with mileage and power. While it won’t be a tire frier, you could enjoy a 260+ hp 318, 300+ hp 360 and still get mileage.

An overdrive trans would pay dividends if it stays there for the duration of ownership and allow for a change of gears for more get up and go.