I would say that there are a lot of different things you could do to an "old-school" Bug. I think .18 Cd is a little on the optimistic side, i would set a beginning goal of .25-.30 Cd. Then again if you look at basjoos's Aerocivic, you can drop it down quite a bit. i would drop the ride height for starters; depending on how tall you/your passengers are you might want to chop the top down a couple inches. a boat-tail is pretty much a given, maybe you could extend the wheelbase back a little to help weight distribution(though that could take quite a bit of work)
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