Today's post deals with the interesting case of a concept car intended to demonstrate even more extensive panel-sharing. It is the 1966 American Motors Cavalier (Wikipedia entry here). Besides the below-the-beltline parts of the doors, the front and rear side / fender panels could be used on both sides of the car. Also the bumpers, front and rear. The link above claims that hood and trunk panels could be interchanged, but that isn't evident to me from the photos.
The resulting design is fairly clean and attractive, though diminished by having a static feeling that was probably inevitable, given the quest for symmetry.