Sorry, can't really help you there. You'll just need to get up in there with and O2 sensor and bung to see where it could possibly physically fit, and mark the location. then you'll most likely have to remove the pipe to do the drilling and welding. Also consider installation. Will there be enough room to install the pipe with the sensor pre-installed? Is there enough room to get a wrench up there to tighten the sensor if you need to install the sensor after installing the pipe?

Also, by installing a sensor there, you are only monitoring one side of the engine. Is this good enough? Should you install a sensor on both sides?

And is it safe to install a wideband O2 sensor that close to the head (location of highest exhaust temps)? Might want to talk to the O2 sensor manufacturer about that.

Why don't vehicle manufacturers just use wideband O2 sensors to begin with? Seems like they could design the engine control systems to more precisely control fueling if they always had actual fuel ratio feedback, rather than only using narrow band sensors to target stoichiometric mixture when in closed loop.