Howdy All:
Thanks for the kind words Robert. Here's a summary I wrote down for a fellow Ford Sixer a few years ago. Since little has changed relating to mileage (except the price per gallon) I thought I'd share it.
"Ironically, most of the same mods that make power make efficiency/mileage too. The set-up and details are different though. Ak Miller’s used some of these ideas in a Mobil Mileage test back in the sixties along with some others like rock hard tires and extreme driving techniques to get well into the 30 mpg range.
Head: Higher compression, up to 9.3:1 (Real, not advertised}, stock valves and springs, and ports, three angle valve job and back-cut on intake valves. We recommend a port divider to improve cylinder balance. Mileage efficiency is a situation where a mid 60s 170 head with “Kidney” shaped chambers may have some merit. Smaller ports=higher velocity, smaller valves=higher velocity and vacuum, Smaller combustion chamber= higher compression, higher quench area to bore ratio for better turbulence and combustion efficiency.
Cam: Stock, or a specific mileage grind that maintains high vacuum and a low rpm power and torque peak. Caution- high CR and stock cam timing makes for high cylinder pressure and head. Make sure it is managed.
Exhaust: Stock, with a turbo type muffler. Although backpressure is not good for economy, neither is too much scavenging. The stock exhaust manifold helps to keep heat in the head and warm the carb base. And this will be a low rpm engine.
Ignition: DUI, DuraSpark, DuraSpark II or Petronix upgrade in a distributor with vacuum and centrifugal advance (68 and later). Set initial advance just shy of "knock". Note- The carb vacuum signal must be a correct match to your distributor. SCV to LoM, Ported signal to ’68 and later distributor.
Intake: 1st choice (with a DuraSpark II) for economy-two stage Holley/Weber, tuned to your situation.
2nd choice, With Load-a-Matic points type distributor- Use the smallest SCV one barrel that can meet the load requirements. Use some form of heat to the base of the carb, either hot water or hot air. Heated air to the carb helps with fuel atomization for more efficient mix with air and combustion.
******Under any circumstances tune the carb as lean as possible, but balance with ignition, compression and load. *Minimize choke and accelerator pump function.
More irony; All of these mods and parts would buy a lot of gas. Start with what you've got; optimize the initial advance setting on your distributor, make sure your carb is as lean as possible, not over-choked, low float level and there are no leaks, either gas or vacuum. High temperature makes for more efficient combustion and mileage. Do everything you can to keep the heat in the engine. Try a higher rated thermostat. Heat must be safely managed.
Make sure; your vehicle is as light as possible, tire pressure is at the maximum recommended PSI, there is no brake drag and alignment is dead on. A taller rear tire will give you a better economy ratio, but you won’t notice in MPG because your odometer won't show the change. Next oil change, try a lighter grade of oil. Synthetic oils make more mileage, but are twice the price. Do not overfill your gas tank and don’t be tempted to top it off. These two practices lead to spills from expansion and evaporation.
Some last thoughts; install a vacuum gauge and relearn to drive by using the gauge to maintain the highest vacuum under all circumstances, never exceed 55 mph, avoid cold starts, preheat before starting when possible. Don’t idle to warm up, just drive slow and low for the first seven miles. Don’t sit and idle EVER!!! Avoid traffic and stop-and-go driving. Slow down and coast whenever possible but be safe!. Keep accurate, repeatable measurements for comparison and records."
Hopes this is helpful.
Adios, David