Use an NMMA TCW3 outboard motor oil, available at most auto parts stores, sporting goods stores, etc. When that motor was built, there were no outboard specific oils. The oils we have today are much better for that outboard than a non-detergent 30 weight will be.
I think for a pre-1964 less than 18hp should run a fuel to oil ratio of 24:1.
Take a look at this link, and change the drop down menu to "Oil/Fuel".