I have a '92 E-150 conversion van, same basic model shown above, but with a high top cap.
http://www.google.com/imgres?imgurl=...=0CIEBEDMoXTBd
Its mirrors could be smaller, and the Corplast undertray idea is very promising since the stock belly of this van is an aerodynamic abortion. Or at least add a garden edging air dam. Pizza pan wheel covers would be s snap to install, nestled inside the aluminum wheel rim lips.
My brother has a Ford F-150 with the same 5.8 liter engine, so it's mechanically the same. He says he gets MUCH better highway fuel economy by changing the ignition timing, i.e., ~18-19 mpg vs. ~13-14 mpg previously, so look into that simple mod.
The E-150 van may have better (less bad) aerodynamics than the F-150 pickup truck.