The 2CV Safari wasn't just a concept. It was actually sold to the public! And there are currently 2 for sale in Germany. For about 100.000 euro (125k in yankcoins) you could be the proud owner of a tin can with two engines and a gas tank inside the cabin.
Are there any other two-engined cars that progressed beyond the concept phase? I know about the 2 engined Scirocco which was just a concept, there are the hot-rod home-builts and mfg-backed hot rods, but as far as I can tell, the Safari is the only production twin-engine car.