building a long distance touring car

I would go 318/5.2... EQ heads with really good valve job and cleaned up ports/bowls. The closed chambers should bring compression up and have a good quench. Get a custom cam ground by good cam guy. Fuel Injection and a Daytona systems ignition..small tube headers..
Then get the FI and ignition curves set to a Gnats *** !

3.23s out back and I think you could see mid 20s mpg.