cat pipes same on '96 thru '98?

[DDubbs]

I have a '96 throwing a check engine light with code for underperforming cat. Car runs great, gets regular highway mileage but reduced city mileage. Mileage was reduced for about 6,000 miles before the check engine light came on. My mechanic asked $3000 grand for a new cat and replacing the 02 sensors. That's not going to happen.

So I got a lead from another member here on a used '98 cat. I didn't realize it's an entire section of pipe and not just the cat until I looked it up on realoem. Here's the link for the part, and now for the question:

The diagram shows two different part numbers for the cat. Can I use a 98 pipe on a 96 car or are the different in some fundamental way? I'm also up for anyone with some experience or information on why the car has run great for the last 4,000 miles with the CEL lit and a supposedly bad cat.

Thanks!