Lightening up a slant

The Dodge Dart Lites and Plymouth Feather Dusters had 300-400 lbs shaved off of them to help the fuel economy a bit, so that is the realm of weight savings for making any real dent in mileage. The weight savings actually did make them move out better. (I drove one for many, many years.)

Those cars got their biggest mileage improvement with the OD trans, and 2nd with the lean carb and other tuning. I haven't exact weights, but I doubt you will save even 20 lbs on the AL intake; the iron one doesn't weight much more than that.

If it mileage you are after, see what you can do to install the 4 speed OD trans. And, the AL case on that will save as much or more than the intake change.