I'm guessing that it might have a 1/8" (.125") propshaft. Wioth a .15 you're probably looking at an Octura X-435. If it has the 3/16" shaft then you can take it up to an X-437.
With your measurements above, an X-432 is just a hair over but should be too small for that boat-engine combo. A weak stock electric motor will spin that.