Unfortunately, you don't have an "Option" on which one you buy. You have to inspect your Jeep first to know if you can, and here's how: Open the hood and take a look at the vehicle ID plate that is attached to the firewall, right by the brake master cylinder. If your vehicle ID plate reads something like, "This vehicle conforms to CALIFORNIA EPA standards" or something like that, CALIFORNIA being the important word, then you HAVE to buy the CA compliant converter. There is also a number or something that has to match the number on the CAT too, but I can't remember what it's called.
On the other hand, if the vehicle ID plate reads, "This vehicle complies with US EPA standards" then you can buy the cheaper one. How do I know this? I did my research about six months ago when I had to buy a new one.
In SD, I went to Express Muffler and got most of the info...they are always pretty cool. Give them a call for more on the number match, also check DMV website, I remember they had some stuff in the FAQ section. (619) 449-6800. Gotta love California! :doh: