Simply add on an after market cooling ring and flywheel and you have a marine engine. There is/was companys that made parts to convert most any airplane engine to marine use. One thing that is weird about your engine is the lack of the word "Fox" on the side bypass bulge. Also the bulge doesn't go all the way down to the mounting pad. I wonder if some Asian company ever made knockoffs of Fox engines years ago.

Later,
Tim