Bob, in the pre-emissions days (prior to 1974 from memory) there were a few Japanese models sold here with the low compression export engines, so they could run on 89 RON. I don't recall any from 1974 onward.
I don't subscribe to your method for calculating oil to petrol ratios. I agree that changing the oil ratio will change the air fuel ratio a bit, but that is accidental. You put in the percentage of oil that the development team at the factory found necessary, then you size the jet to get the air fuel ratio you want. It is no trick at all to change the jet size: you just solder up the brass jet, and drill the size of hole you need. Jet drills come in size increments of 0.001". I've never felt prosperous enough to buy a full set, I've just bought a few in the immediate vicinity of where I expected to find the right answer (and usually lost them soon after the job was completed). You use a combination of clues to get it right: sound, maximum RPM, standing quarter mile time, and plug colour. Of course if you've modified the engine you get the plug colour right by changing the plug heat range, so you can't use that one as a clue for tuning the mixture. I did once use a different system for adjusting air fuel ratio, but it was just luck that method was available. My brother knew someone with a Non-Dispersive Infra Red oxygen analyser, and we used that. You can achieve about as much with an NDIR carbon monoxide analyser. The right equipment certainly makes a lot of jobs easier.
