[ByronRACE]

OK, then define your requirements. Start with required rear-wheel horsepower and required gas mileage. When you find your happy compromise, I can make a suggestion.

400rwhp and 30mpg is unrealistic from a Ford V8. Both can be obtained, as well as more extreme examples, but they are generally mutally exclusive.

One thing is certain; if mileage is a requirement you should be looking at modern EFI systems. And, if both power big and good mileage is a requirement, you should be looking at EFI power-adder combos with active air/fuel feedback using turbos or centrifugal superchargers that are minimally parasitic at low-rpm. And, tallish rear-gears 3.00 or taller, with an overdrive manual transmission will help as well.