Help ID 80’s Johnson

[Truenorth2000]

Hi, I’m new here. Looking for assistance to identify this motor. It came an old sail my boys and I are working on. It appears to be a well used 80’s model; I can’t seem to find anything to indicate model or serial number. There is smallish flat are on the transom mount that may have had an I’d sticker but it’s gone, I don’t see anything embossed or tagged to ID. It is a two cylinder, I’m thinking 10-15 hp.
Also what would be preferred oil:gas mixture.
Thanks for any help.

 

[racerone]

My best guess is an 83 model or 85.

 

[tphoyt]

I would guess early 80’s as well sorry I can be more specific.
50:1 on fuel mix