There is really not much to do. Store the engine upright. It is self draining and there is no freezing danger if stored that way.
You can "fog" the engine if you want but that is not really a necessary step. To fog, run the engine on muffs and squirt fogging oil into each carb for a couple of seconds
Now would be a good time to do some preventive maintenance: Change the lower unit oil and inspect the oil for water. Free water draining or milky oil indicates a bad seal somewhere so all must be checked. Drop the lower unit and replace the water pump impeller. Iboats store will not carry an impeller that old so try Valley Sales or
franzmarine@aol.com