I have a '69 f100 with 107k original miles on it......recently with everything still being original i've had to replace the distributor, starter, solenoid, master cylinder, alternator, etc.. I have also added a K&N air filter and a single Flowmaster muffler with a y-pipe for duals running out the back....These things have upped my mpg and also made the truck run better than ever(not that it didnt run good to start with).....i've been doing some research and i've found the offenhauser intake manifold that converts to a 4bbl carb. instead of a 1bbl., also a comp cam., and a pacesetter header for my engine.....just wanted everyones thoughts on how much of a difference these things would make as far as gas mileage and performance?? and also if it would be worthwhile to invest in these things? Thanks