After my negative FE results above, I decided to revert to something more akin to the coveted 1969 Dodge Charger Daytona. It has the same (or nearly the same) frontal area as the "normal" 69 Charger, but the aero shape gives it a MUCH better Cd.
The Plymouth Superbird and Dodge Charger Daytona, supercars (15% better...)