Improving the Aerodynamics of a bug is an interesting idea. I am familiar with them I have one and also used to have a baja. What ever your car gets FE wise is better then my high performance engine with dual carbs.
The biggest issue with aeromodability of a VW Bug is the fact that you cant do anything that will effect air flow, not enough air is death to an air cooled engine.
Also I have never used a freeway flyer trans but many people don't like then because of the fact that they lower rpms. Lower rpms of engine = less rpm of cooling fan.
If you have never seen
TheSamba.com its dedicated to old vws you will find lots of information and help there.