I recently got the p0420 code and narrowed the issue down to needing a new cat. Thought i'd be smart and went to Walker identify the exhaust for a basic '04 Nissan Xterra XE, 4WD, 3.3L. Found the parts for the manifold cat, boom, purchased from Amazon. Thought I was on the road to repairing this, part comes in, take it out to the garage to drop off the cat and low and behold they don't match!
I purchased this puppy: Walker 16500.
But when I went to match it up. It looks like the manifold cat and the manifold are a single unit. They certainly don't have the triangular flange as indicated. See picture: 
I then decided to search for the exhaust manifold, assuming that the vehiclle/model had a singular exhaust manifold/cat and only found an exhaust manifold that appears to match the cat manifold that I purchased (and was incompatible with the installed exhaust manifold). What have I missed?
