Best place for Wideband O2 install w/ cats

Hi all,

First, thanks for all the great content here. I've been learning a ton.

I'm running an GM LFX V6 swapped into a Mazda RX8 and looking for advice on the best place to install a wideband O2. The LFX has integrated exhaust manifolds so only down pipes. I have high flow cats only a 18" or so down on the downpipes so there isn't a lot of room for a wideband before the cats. But there is one place, on only one of the downpipes, shown circled in red. The other pipe is a shorter run and doesn't have the extended part so I'd only be monitoring one bank.

I've also heard mixed things on running after the cats. That'd be a heck of a lot easier if it works. I have an X pipe and could get a reading post X which might be good for getting both banks, but again, after the cats.

How bad is monitoring only one bank? How bad is running the wideband after the cats?

Also, I think I only need/want the O2 installed during tuning/logging so I dont think I need an actual gauge or a permanent install. Do you think thats reasonable or do you think it's useful to have a gauge always there?