454 to be or not to be??? For my son

[BigDan3131]

All that being said your/his mileage will depend on gearing and the transmission more than whether or not its a BBC or SBC. Without the right gears it will be a dog off the line and also eating more fuel, add to that a small block that's built stock with a holley 2 barrel and gas mileage will suffer because of it. But since he's spinning the tires now it must be geared right otherwise it wouldn't. Keep the 454 but just go to a 600 cfm carb as you will lose power due to it being smaller and then just put a good OD trans in it.