B3S1 covers the section of the exhaust highlighted in the attached image. That is on the right side of the engine as you look at it from the front.
The part number you gave is correct for the CTNA engine.
In terms of where the connectors go to, check out the following PDF, starting from page 276. From a quick glance at it, it appears that all the connectors are located under/behind the air box on the right side, which in itself is under a metal brace bar. There is an image on page 32 which shows what all the eight connectors go to.
13-Service Manual 12-cylinder direct petrol injection engine (6 3 ltr 4-valve).pdf
As mentioned previously, once you've located these, I would disconnect plug number 7 (G285), take the car for a drive and rescan. In theory, you should ger a different error for B3S1. If you do, then that is the correct connector, so you just need to follow it to find where it connects to the exhaust.
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