Daily Driver.. LA318 vs 360 Magnum
I daily drive a Quad Cab 4x4 Dakota with a 5.9 Magnum and it gets an honest 15 mpg with norm driving. Of course thats EFI, but still that's pretty good. I would guarantee if the tune is right you could get decent fuel mileage with either engine. If it were me, I'd build what I had if I was shooting for a mild street engine.