16:1 for your MD-39! Originally Johnson called for heavy #40 oil for the mix but that was probably to help seal the crankcase bearings more than lubricating the motor. Current TCW III rated outboard oil is quite thin, about 5 or 10 weight and is meant to flow thru injectors when cold but it lubricates just fine. Go with the 16:1 and you’ll be OK.
High octane fuel is meant for high compression motors and it burns slower in the cylinder than regular or lower octane gas does. The slower burning is to prevent fuel knock or preignition and using it in a low compression motor is kind of pointless as it costs more and as already mentioned, can cause a loss of power compared to using the recommended lower octane gas. Save the high octane gas for airplanes and race cars!
