Well, obviously I've been beaten by a full day on this call.
So I can't add much to the story told in the other thread mentionned above. I have pictures of those boats, including one where Alfa mechanics are fitting the engine into the boat (don't remember which one, would say a Laura). Note that marine competition have also been successfully prepared years later, by Autodelta, with 4-cylinder engines and 33 V8s.
Prewar, a 12C36 GP engine was also fitted into the "Mariella", Passarin's boat, as quoted by m.tanney in the other thread.
An even odder boat racer, fitted with an Alfa engine, is to be seen in the basement of the Science museum in Milan. Guess the engine...