I've answered my most critical questions, so I'll share what I've learned:
I am a bit surprised nobody on here would at least verify that the upstream sensor is an air fuel sensor (essentially a wideband) rather than a standard sensor.
This post on the Honda-tech forum explains what I am seeing:
https://honda-tech.com/forums/honda-...whack-3272201/
So, nobody switched the sensors but it remains likely the cat is not too happy--again, this is not a big surprise as the car is known to have been burning oil. On the other hand, it's also clear that the cat design and implementation here is not Honda's brightest moment, as my research seems to indicate that cat problems are one of the most common issues with this car. I don't have a stock cat to look at, as I suspect the one on this car is not OEM, as it is, I think, the third one, but I believe even from the factory this was a "high flow" design with concentric metal layers rather than the ceramic honeycomb. It is also tiny, and the downstream sensor is smack in the middle of the cat. I am not about to try it just yet, but I wonder if the best solution, at least from an emissions standpoint, would be to simply retrofit a larger ceramic cat with the downstream sensor bung in the far end rather than the middle.
It seems that using an drilled out anti-fouler as a spacer for the downstream sensor, even on a good cat, is what everybody does to keep these cars on the road, so that's what I'll do next and hope maybe the cat will also clean itself out a bit if I can keep the oil out of the combustion chamber. I haven't really driven far enough to verify that, but so far so good.
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