AMC was the perpetual underdog of America's motor industry, and the only reason they survived as long as they did was because they were so damn clever. And by "they" I mostly mean designer Dick Teague. AMC was always strapped for cash, and Dick was a master of cost-cutting. His masterpiece of cost-cutting was the AMC Cavalier.
Back when AMC was still Nash/Rambler, they were already trying to cut development and manufacturing costs for cars, and the idea of stamping body panels that could be used in multiple locations was one of their big ideas. It was first put to use on the little Metropolitan, which used basically the same panels for both doors. In 1965, Dick Teague pushed this concept to the extreme with the AMC Cavalier concept car.
The main driving force behind the Cavalier was the idea of symmetry and with that, body panel interchangeability to a degree never before seen. The Cavalier was a four-door, with suicide doors at the rear so that the same two basic doors (left and right) could be used for all four positions. The hood and trunk lid were the same panel, as were the opposite-corner quarter panels (again, two stampings for four parts) and the front and rear bumpers were the same as well.
The overall look of the car was actually quite clean, handsome, and modern. Largely unadorned and unornamented, the car also had some novel features. This included a trunk lid on special scissor hinges to allow it to raise to roof height for carrying bulky items, like an open station wagon of sorts.
The design ended up being a bit too radical for actual production, though the basic look and design did carry over into the production AMC Hornet. And the AMC did use a little bit of interchangeability, with the front and rear bumpers being the same on some models.
Plus, they really put the idea of parts reusability to the test when they basically made their compact car, the Gremlin, by chopping the ass off the Hornet. That's pretty efficient.