any body building a mopar for max mpg?

I know we all love performance,but is anyone on here building,or have built a old mopar for maximum gas milage?Im sure a slant six,or stock 318 would be the best,with a 2.76 gearset.What i want to know is,whats the rest of your combo?If running a slant,is there a od auto that bolts up?Or is the od 4 gear the only option for extra milage?On 318,is there a 4 barrel carb thats better for gas milage than the factory 2 barrel?I noticed my old thermoquad had smaller primaries than the original 2 barrel i took off the 318.Is there a way to keep the secondaries from opening,incase my foot gets heavy?lol