Cummins mpg vs 225 Slant 6 mpg

I need some opinions here. I have found two trucks I like equally, and are the same price.

first one is a 1974 d-100 single cab stepside with a 225 slant 6 and 3 on the tree manual. cons are torn seat, cracked dash, and needs tires.

second is a 1982 d-150(ram) single cab stepside with a 5.9 first gen cummins. cons are ugly hot rod flame paint job, not sure if it can pass emissions.

my main deciding factor is gas mileage as this will be a daily driver.

but... the '82 has a nice of weld bullethole wheels, 3.5" rims 4.5" tire skinnies up front, and 8" rim 10" tire fattys in back that would look great on my scamp. I'll just put my Rallyes on the truck.

opinions?