Stock replacement cat?

So I did search and after quite a while I think I settled on 1.75" being the OEM base model diameter... probably... maybe. People on here contradict each other like crazy. But anyway, I'd rather not pay out the ass for a direct fit cat and just get a universal one welded in. Trouble is, I'm not finding one with the 02 sensor bung in the middle of the cat. How important is that, exactly, over having one welded after the cat? I'm getting a new one (I think I'll replace the sensor as well while it's in the shop) because I'm getting the code for a bad cat, P0420. I'm not interested in high-flow or performance anything right now.

I hear Magnaflows aren't good for passing more than one emissions test before going out, so I've been looking at

Walker
http://ift.tt/2esS0WY

and Catco
http://ift.tt/2esS0WY

Stock replacement cat?