318 magnum VS 318 roller VS older 318 gas mileage

If you're not planning to rebuild, but looking for a lower mileage replacement engine, then I agree with the Magnum choice for gas mileage and longevity. There will be extra initial costs as far as balance/flex plate issues, and front drive pieces, but in the end I still think you'll be money ahead on the overall swap for what you're looking for.