SuPer SiX Slant Signet!

I hope a crank kit would be OK.
I'm rolling the dice and will drop the pan in the next day or so
My main goal is getting the Signet to the best mileage possible
as this car is my daily driver now and may evolve it to something else once the Dart is done.
I will have back surgery and need to have an auto in there until I am healed so I got the 225 slant but I have a 273 2 barrel automatic too
I know what combo has more power here but what would be better for gas?
I am 47 yrs old and can keep my foot off the gas so with a light foot what would do better 273 2 barrel
or a super six 225
I only have one shot at this then I will have to live with it until I am healed and probably after next winter so everyone's advice would be appreciated!
thank you Fabo!