It is the 1957 Trippel Alligator, which was developed into the 1959 Eurocar Alligator, which first kept the center steering, but later changed to LHD. It finally emerged as the well-known Amphicar. To date, this is the only information and picture found of this rare, amphibious car. If more is known, please comment below.
Source & Image: AutoPuzzle (2015) https://www.autopuzzles.com/forum/2015-44/solved-neh-4199-trippel-alligator-amphibious-car-1957/
