The Intrepid already has a good cD I believe. I remember reading back then about how various styling elements were created for the sake of aero, like the high trunk.
I wouldn't buy a vehicle with a plan to build a big boattail. I don't think it's ever really worth it. Ask yourself if you are really going to make something that looks anything like the photoshops, much less a professional rebody.
90s cars were aero enough.
How about an Oldsmobile Aurora
Edit: Site with pics hassling about hotlinking
