Here're a couple of things:
There're other instances of movies using VW for stunt vehicles ('Corvette out of a railroad car in F&F, for example)
This has the predecessor to the Schwimmwagen at
3:29, the
[wikipedia]Trippel_SG6
IIRC the Trippel Amphicar was powerd by a water-cooled engine to satisfy the U.S. Coast Guard.