Super Six fuel mileage

Yeah Slant6.org is where I have been reading up on a lot of stuff including how to mate a T5 from a 4 or 6 cylinder Mustang but the bad part is a rear gear change will have to be done. Can you think how much fun that /6 will be with EFI and 5 speed?

A mustang trans will bolt up to a /6?! You have my undevided attention!