[Signman]

Hello all hope I can positively add to the conversation:

It's good to ask for advice but what works for me may not be optimal for you or even useless.

The proper way is to take the car to a chassis dyno with good tuner. Tune it for maximum power to the wheels, isn't that what is the ultimate goal? While doing so observe the AF ratio and carry that to your AF target map. You will now know what is optimal for you with all the various factors of choices made.

Locating the O2 sensor in the collector will see the average of all four cylinders but will appear lean due to reversion pulses of fresh air you cannot do much about.

When placed further up the primary tube closer to the exhaust valve there will be much less effect from reversion pulses AF will be slightly rich compared to in collector. You will see reading only from that one cylinder.

We did a test on the engine dyno with O2s in all 8 just to see how balanced or out of balance fueling was cylinder to cylinder and then do some individual cylinder tuning. What we found in my case (TPI) we were in good shape.

Then of course old school reading plugs really is not old.

Be Well!