In my recent desert trip one thing stood out, I'm getting horrible gas mileage. I used 12 gallons over 2 days while my buddies 1.6 powered Samurai used 5 gallons. Not sure how many miles that was as my speedo isn't hooked up yet. I've been looking for a reason to get rid of that 1 barrel carb, I guess mileage will do. My 4.2 already had a Davis Unified HEI ignition on it when I bought it. I've read a swap to a 2 barrel like the Motorcraft 2100/2150 will improve mileage and performance. Today I picked up a later model 2 barrel manifold to get started. Now my decision is; do I buy a Header? Or buy a later model cast exhaust manifold? With the header I could go to a 2.5" muffler and piping. What say you? Any advise, concerns, ideas?