What mpg does your old 'stang get and how can it be improved?
While the '67 289 wasn't a great mileage car it should do considerably better than 14 MPG. One thing to do is to power tune it. Forget the timing light, except as a starting point. Most Ford specs, on those engines, were way too retarded and the engine will run much better advanced. Use a tach, if you have one and slowly advance the timing until peak RPM is achieved. Another way is to advance the timing until the engine stumbles then back it off slightly. You might also consider sending the carb off to Pony Carburetors in Arizona for a rebuild and update. They can improve the performance of most of the old carbs and ill return it looking like it just came out of the box. A pertronix transistorized will also help by increasing the spark and have the additional advantage of no points to replace. Since it's all contained under the distributor cap it still leaves the engine looking original. A good rebuild of the distributor will also help. Ford only put one bearing on the shaft and it has a tendency to wobble, especially after years of wear.Ignitioneering in Fullerton,California rebuilds them to spec but adds a lower shaft bearing to stabilize and improve the performance. Your driving habits are important too. Jack rabbit starts and hard, last minute braking will detract greatly from the mileage. Another gas guzzling item, on these old cars, is the AC. The piston style compressor on them loads the engine heavily and guzzles gas. Switching to a modern rotary style compressor will get rid of some weight and greatly decrease the load on the engine. It won't look original but you can always keep the original in case you ever want to restore it. As far as original parts go, they're few and far between and extremely expensive, when you can find them. However, a lot of the after market parts are now being made using the original Ford molds and specs under license from Ford. Look for "made from Ford original tooling" in the catalog, especially on sheet metal parts.