you are looking to utilize only the exact amount of hp to propel vehical along at 70 (or whatever your desired cruise speed) mph. Whatever that btu energy requirement is, is what the carb needs to provide as efficiently as possible. Carbs are very efficient on their main metering systems, and quite possibly most have nearly the same efficency. Carter carbs pioneered the vaccuum advance in the 20's and it has proven to be an improvement of 20% in economy. I would set total advance to be just shy of bucking at constant speed, probably needing the vaccuum advance to have only limited travel (bent nail in slot behind canister, 1/8 inch dia.) to allow for a little carb loading without pinging, oh yeah use ethyl (premium grade for you youngsters).
Ak Miller, its said of, used to air up his tires to 50# (pre radial days), run vaseline as wheel bearing grease, use light weight rear end lubricant, and back off any drag from brake shoes etc. to an effort to lower all mechanical drag. Who says you cant coast down hills? You may even approach 40 mpg and have the oil companies buy your car from you in an effort to crush all such techonology (you know how they are, i.e. fish carbs etc type wives tales)
