Johnson built a pump after 1950 for the Navy with an aluminum frame with a spot for the tank on top of the frame. It used the 25 hp Johnson powerhead of the era. See the carb knobs, they appear to be the same as the 1953 Johnson 25 hp outboard. My guess that this tank is for this type pump. I had to dig in the backups of my files from 2000 to find this picture.
Don
