[olddog]

I will toss out another thought, but I doubt this would be acceptable. I am assuming this is a 427 FE and not a Windsor based engine. If so pull the FE out and replace it with a stroked 5.0. My 347 gets about 15 MPG just driving around. I estimate it makes around 400 HP or a tad more. Dwight drives to the London Ohio Cobra show from Alabama (I think). He told me he gets around 20 MPG on that trip. He can correct me if I'm wrong. We both have stroked 5.0 engines with EFI.

If the OP is indeed getting 9 MPG then a 17 MPG 3 year return on investment would be a budget of $5100. If you sold the FE engine this would be easy to do. However anyone who has a FE 427 SO is not going to like this idea, unless they want to drive the car a lot and do not care about the legacy of the car