Slant 6 MPG Upgrades?

Just to be the devils advocate here, I see everyone discussing directly modifying the /6 (with good reason) but as I am sure you are familiar with the "Feather" duster and similar a bodies of the mid-70s, much of the gained economy came from weight reduction. I see that you are already on the way with the lighter weight engine components but the same way you can cut drag times to make your car faster at the strip with more power, you can have the same effect with less weight. That applies to mpg as well, the less weight you have to move around, the less power it takes to move it. Have you considered any type of fiberglass components? At bare minimum bumpers and maybe even fenders, hood, trunk lid?
Just a thought...