That's a nice one, ady. They're a classic airdrive for small boats, and they were first produced in 1954.
According to my materials the Air-Boy was made by Airboats, Inc. of Denver, CO. They were available in 2, 3 1/2, 4, 5, 9,
and 12.9 (twin cyl.) horses, and were built well into the 1960s.
Yours looks to have the A-100 Power Products engine which was rated at 3 1/2 hp, I think.
It's a neat little package that has been copied by a lot of other builders, including Mosquito, since.