Here are two more proposals. Aerohead likes Carl Breer's work at Chrysler, so the one in the back is a superelliptic stinger, with the fenders flappin' in the breeze, to mimic that design.
In the front is a boat-tail that's very aggresive in taper. But at the tip are vertical Coanda nozzles that have hot engine cooling air routed to them. It's a toss-up whether that would pull more air through the cooling system, or offer additional back pressure.