Oppps, Moderation Failure, sorry Straight Six. I messed up your post. I'll try to fix it up.
Welcome. I'll try to keep the Techno Bable levels low, but I'm a BableOn-ian, so you've been warned.
stick with the domestic
stick with stock i6. The 200 is always more economical that any similar 250. Always. Engine weight varies only from 330 to perhaps 480 pounds. 150 pounds costs 0.5 miles per gallon. Engine Weight reduction Not worth a darn.
Stick with 1-bbl stock or any small 2-bbl carb
Best, most modern electronic ignition money can buy, and good spark plugs
Any cam that has what is called Advertised Duration at Lash which is more than the stock 252 or 256 degrees and up to or including 272 degrees won't hurt fuel economy at all. Best is a 264 degree item. This is a proven fact from years of exhastive testing in the engine industry.
EFI is the best for fuel economy, but it must be an expensive port injection system with a MAP sensor. None exists yet as a bolt on unless you opt for an alloy head or alloy head engine.
just has to have a FSPP/Classic In-lines, Hooker, Pacaemaker, or Clifford header, a port divider, and a small dual out exhast pipe system of the same specification used in 289 'K' code Mustangs.
Best gearbox for economy is a domestic T5 manual. No if butts or maybees. If you are going to use an automatic C4 auto, you'll loose 2 or 3 mpg. If you want an AOD, you'll have to wait for an adaptor to be available or use a 1981 onwards 200 engine, and you'll never, ever get better economy than a T5. A Toyota 5 or 6 speed, Ford T56, or Ford/ZF 6R gearbox is an expensive option, which won't be worth the effort
Yep, maintain rearwheel drive. Front drive only saves 150 pounds , and half a mile to the gallon, and the car has to be desiged as a front drive car from the get go.
Go up in wheel wheel size, and use the narrower section size. Some 205/60/R16's sound okay. Modern low profile tires are better than earlier "75"
(american racing equipment ...ARE great)
fiberglass--hood,trunk lid are around if you search. They are not cost effective, but can save 200 pounds or more.
Sorry buddy, but Do Nothing Unless It Saves Fuel. Then be happy with every cent you spend. It costs more to save fuel than it does to just pay the extra price in gasoline each year. That's a proven Fact. The best way to make a Ford Mustang go from 18 mpg on the highway to 50 miles per gallon is to buy a used diesel Volkswagon Jetta.
Get an aftermarket, 68 on wards fuel tank. Its about 17 US gals or more No to aluminum drive shafts
Best rear end is the 2.79 or 3.00 or 3.25:1 8 incher found in Mavericks and possibly some Granada's
