Found this little tidbit from near the bottom of this page:
http://www.amphibiousvehicle.net/amphi/P_P.html
Pontiac M-76 Otter (1952)
The one in the top picture was built in 1952.
Production started in +- 1942 and ended in +- 1953
As fare as know by Johnny (he owns the one in the top photo) there are only about 200 operating otters left.
Engine: air-cooled 4 cylinder Continental AD-268 130 hp
Gearbox: Allisin CD-150 2 forward 1 reverse
Speed land: 50 water: 7 km/h
Length: 5150 width: 2690 height: 2640 mm
Tracks: 750 mm wide
Load: 2500 kg
Water propulsion: (folding??)propeller at the rear
Constructed from aluminium
The info and pictures where send in by Johnny Willis.