Sometimes the Flinstones are just right for an old car!
If you're looking for a gas miser and look towards modern engines, you might also look at some modern 6 cylinder engines. The modern stuff has a lot more power than the older stuff, and you might be able to save even more gas. However, there's also the point of the V8 having more power and able to run more efficiently at lower throttle (sometimes).
My uncle just bought a brand new Dodge 1500 truck (Hemi 5.7). He says it gets better mileage than his previous, a V8 Dakota--and likely a lot more horsepower.