Suggest you go to this site for antique outboards:
The Antique Outboard Motor Club Website - AOMCI.org If you post your motor pics there, someone can help you probably.
Dad had a SK 12HP, which was a 2 cylinder outboard. It ran quiet. My GUESS is it was about a 1950 model.
From memory of it and the pic of yours, I'd say yours is pre-50.
Ours was water cooled, and ran smooth and quiet. I thought all "modern" (including yours) motors were water cooled and used impellors, but I might be wrong.
Ron