Bore size versus fuel mileage. 273 versus 5.2 magnum

So the price of gasoline has me rethinking the plan of a mild 5.9 8
In my arrow pickup.
Now I'm thinking since its the lightest vehicle I own I should make it my daily driver and build for a little fuel economy.
I have a magnum 5.2 that needs rebuilt but that got me wondering about finding an old 273 also.
I need it to be torquey because daily driving for me is in the hills of western pa.

But which do you think would be better for mileage and why?