DAY4-Checked the 79' Johnson 100hp Javlin owner's manual regarding
octane:

"RECOMMENDED GASOLINE - Use gasoline with the following minimum octane
numbers - 1) Pump Posted Octane Number 86 2) Research Octane Number
Most Commonly Used in the Past 91"

and

"Automotive gasolines regular-leaded or lead-free meeting these minimum
octane numbers may be used; however; best results will be obtained on
35hp and under by using lead-free gasoline"

Johnson Outboard Oil / Gasoline Mix:

1 part of approved lubricant to 50 parts gasoline - 50:1
1/2pt (.23 litres) for 3 U.S. Gallons(11.4 litres)
1pt. (.46 litres) for 6 U.S. Gallons (22.7 litres)