The advantage aluminum offers besides trivial weight savings is the added heat diffusion properties of the material over OEM steel. Your air/fuel charge will be cooler when it hits the combustion chamber, providing added power = improved mileage. This type of modification is one of a set of things that can be done to spend little money and improve power by cooling the mixture. That was the thinking behind the Thermoquad carb design using the phenolic resin bowls.
Happy motoring,
David
'91 K-Imperial driver '66 LeBaron dual air and every option known to man