22.5MPG on a 1969 gas model is NOTHING to scoff at. Considering what vehicles of that era averaged, that's SUPERB mileage. That's better than any modern SUV can imagine to get, and probably only slightly lower than most modern sedans (My Intrepid gets about 25 all highway, 23 mixed). I'd be far more than pleased with that. Being that you're used to diesel, it may seem like low economy to you, but that's pretty damn efficient for a gas engine. If you REALLY want better mileage, about all that would really help is an overdrive tranny or a diesel engine. Replacing the dual carbs with a single Solex might hurt, being that you'd have less power so you'd have to "Floor it" a lot more to get it to go (although since you're used to those diesels, you might not care that it takes ages to get your speed up). The cost of replacing your setup now with a single solex (manifold, carb, misc parts) would cost you more than what you'd save in gas costs over 10 years!