318 magnum VS 318 roller VS older 318 gas mileage

I'm looking for gas mileage input ( not my cars faster than your car)
In comparing a 318 Magnum with a carburetor installed gas mileage/ compared to a 318LA Roller with a carb/ compared to an old 318LA with a carb.
I know that all things can not be equal (trans/gears/ DRIVERS RIGHT FOOT/ car weight ETC)
But which of the 3 engine combs above seem to get the best fuel mileage. I'm looking to replace an old worn out 273 SHOT cost to much to fix. And finding the most BANG for the buck best gas mileage combo is were I'm headed. No big lumpy cams. Just high vacuum and just a reliable driver . Doing this on a budget.