If it were my vehicle, after making the investment in a wide range AFR sensor, I would make the best use of the $ by installing eight bungs on all cylinders. After measuring and getting 8 cylinders balanced to your preferred tolerance, leave the AFR either in the “most average” cylinder, or in the leanest cylinder if you fear detonation on some of the future fuel you might have to use.
Have you ever tried to tune with an O2 sensor in every primary tube? You will spend so much time for zero gain. It’s not worth it. And the O2 sensor is not the total answer. You can get lost very quickly with it, it will fib to you and not every sensor will read the same.
It’s a tool and like any other tool of that sort it has its limitations. I’ve watched guys drive themselves nuts chasing an O2 number. You still need to look at the plugs, and then tune to those and the O2 numbers are what they are.
