Replacement Catalytic Converter Questions

I have a P0420 code that is not going away. Been going through a lot of threads on replacement cats and it seems aftermarket fitment is hit or miss.

I'm debating keeping OEM, spending the $$$ and ensuring good fitment and function vs. aftermarket. I want to keep the system stock (no removing secondary cats, long tube headers, etc.). A few questions...

1. P0420 is "bank 1". That is the passenger side, right?
2. Should I also replace sensors (oxygen sensor? any more?) at the same time?
3. Rockauto has 3 groups. Among big names, "OE fitment" has Walker and Nissan OEM. "Improved design" has eastern catalytic. And "aftermarket design" also has eastern catalytic. Anyone know what the difference is between the 3 groups?
4. For those who have had this work done at exhaust shop, how much did it cost you?

Ultimately, I just want something that is gonna bolt in without having to shave things down or pull on something hard because a weld is off by a few degrees. And I want it to last. Am I stuck with OEM then?

Bank 1 passenger side. I remember it by cylinder 1 spark plug. which is the pita to get to.
I went with oe primary from partsnissan.com and Eastern secondary cats. Having gotten nearly 200k out of the originals and seeing most people say that aftermarkets fail or start throwing codes after 30k to 50k miles or so, it seemed like the way to go. Fitment was good, but I would deal with some fitment issues if they would last. I did not replace the sensors. They seem to be fine and no codes at 235k miles. I think the shop quoted me $800 in labor only to install all 4. Had a friend help me with it. Hope that helps.
Edit....got them from partsnissan.com.

I would go OE. I used Magnaflow and in 40k I'm throwing codes on the Bank 1 Primary again. Swapped O2 sensors from side to side to verify it wasn't a failing sensor and there was no change.

Plus the OE cats use studs and are a LOT easier to install because of that. I wouldn't worry about secondaries unless your area does the sniffer test.

Cool. I think I can get behind OEM for ease of install as I'll have this truck another 50k+ miles (assuming I don't destroy it before then).

Anyone know what the difference between these 4 on rockauto is? We have a "front right" which probably equates to upper passenger with no core charge. But there are also 3 more with core charges that are "uppers" or "fronts". Are both sides interchangeable? All are listed as a fit for a 2011 Nissan Xterra.

looks like the middle 2 208A3zp51c and 208A2zp51C are the left and right primaries from a part number search on partsnissan. The others look to be the secondaries. Pricing is consistent with partsnissan on the primaries, secondaries are cheaper on partsnissan. It looks like i paid $50 in shipping total for the two plus they included return shipping for the cores. Sometimes rock auto's shipping is too out to lunch.

@TerryD would you suggest he gut the secondary pipes or just leave them be? I threw in Easterns just for structural integrity. May have been a waste, but they were pretty cheap.

Was just thinking... should I be checking something else first before I take the plunge on a $600 part? Or am I just delaying the inevitable? Especially when RockAuto tells me this:



Also, this was the side that I tore the header on. Might this have damaged the cat in some way when the header was basically "open"?

https://www.xterranation.org/index.php?threads/xterra-browns-camp-broke-my-exhaust.9177/