Catalytic Converter without O2 sensor

My local repair shop told me I had a failed catalytic converter on my '00 XJ based upon a code #432. The mechanic explained that the front O2 sensor is slow indicating that the converter needs to be replaced.
I purchased a converter from the parts store and, when I went to put it on, I found there is no O2 sensor fitting on the downstream side of the old converter. The existing O2 sensors are on each side of two bulbous pipe sections coming out of the header.
Can anyone help me with what these sections are? Are they some sort of converter in addition to the main converter?

I don't want to replace the converter unless I can confirm it will help the situation.
Should I use the new converter and plug the O2 sensor port?

The newest xj's had two precats, then the main cat. Those are the bulbous things you are talking about. How many miles are on the truck. Cat's have a warrenty on them so if you are under say 80,000 miles you should be able to get it replaced free, or so I have heard.

If the O2 sensor is slow, I would say the O2 is dead not the Cat.
If you run the Cat without the )2 you will throw a code.

Katarn

Thanks for the response. I thought the bulbous things might have been some sort of pre-cat so I appreciate the confirmation.
The XJ just rolled over 85,000 miles so the emissions warranty is expired. I had it in to the Jeep garage last year (before 80,000 miles) and they replaced a couple of the O2 sensors and said the cat converter was okay.
Do you know anyone who sells the pre-cat? The rep at the NAPA store that sold the converter to me says he doesn't show any other converters on his diagrams.

You can't buy the pre cats sepratly. It is part of the exhaust manifold.