I found out that both of my cats were bad soon after I bought my Jeep. Had already spent a good amount fixing other things, so I went the cheap route.
There is a city called Pasadena about 15 miles from me and it is an auto haven, about 40 - 60% cheaper to fix autos. I wasn't about to pay another 1k to replace those, so I went to Pasadena and shopped around. Came across a hole-in-the-wall muffler shop and looked over their reviews online. Many raved about them and their work, which has a warranty.
I told the owner that I just wanted two new cats at the least amount possible, he gave me three options including OE. I went with middle of the road and got two new, simple ones for a total of $360 installed, never had a problem since.
I don't know the measurements but any shop will know them.