How critical is the Cat & O₂ sensor location?

I'm about to install Pacesetter LT headers & Y-pipe.
The right header has an O₂ sensor bung at the end of the collector, putting the upstream O₂ close to the stock location.
But the Y-pipe brings the left bank in behind the TC, pushing the front of the Cat back about 36".
After the 12" long Cat, I have room for a 24" muffler, and not much else.

1. Will the upstream O₂ be hotter due to the higher flow headers, and will this be an issue?

2. Will the exhaust gas hold enough heat getting to the new Cat location for the Cat to work properly?

3. Will there be an issue placing the downstream O₂ close behind the Cat?

 

No on all accounts. Rear 02 sensor just needs to be behind the cat. Run it.

 

You're gonna want your cat as close to the engine as possible for heating reasons, and the rear O2 as close to everything as possible as well, for wiring length.

 

And your "2" in O₂ should be a subscript not an exponent

 

Good call, Sir. For I had not noticed that.

 

Typography corrected, now back to the topic.

The Cat will be immediately after both banks merge into one pipe, but this is ~36" further back than stock.
Being an "off-road" Y-pipe, I take it isn't intended that there be a Cat.
But to maintain some semblance of "design intent" to meet FL modification laws, I'll include a Cat.
The upstream O₂ is close to stock location, so that won't be a wiring issue.
The downstream O₂ stock location is a distance behind the stock Cat, but not far enough back to suit the new setup... I'm hoping an 18" extension will do it.

Thanks for the input guys!