Daughter needs Gas mileage from 273 commando

You'll have problems with a X pipe and a pre-67 A-body. The torsion bar cross member is only notched on the driver's side. Recommend a 3" single system.

Gas mileage + 273 Commando = LOL. Disconnect the secondary on the carburetor, Dad.

The 65 A-body had a 4" bolt pattern wheel. Sorry, there's not much in the way of wheel selection.

That being said, an easy way to improve fuel mileage is to fit a later model rear end to the car (they all interchange). If your car has not been converted to big bolt pattern axles, stick to 73 and later /6 cars. The gear ratio to look for is a 2.76:1