They are 50 dollars each on eBay for OBD-II compliant ones. 2 inch.

For the original question, I can answer that I experimented on my cats when the left one clogged up. First, I hollowed them. The shape of the driver cat along with the angle of the pipes makes it very loud. Unacceptably so and I don't mind loud. It sounds like a glass bottle rolling down a driveway.

Second experiment. I cut the cats out and put in flex pipe with clamps. I sealed the ends. The driver side leaves very little pipe once you cut at the Weld. Even, as I did, if you cut through the weld and the grind it down to pipe. Further, the noise level is still a little more than you'd want and draws attention to that location and, visually, the lack of cats. Finally, the flex pipe leaves the exhaust in front of the y pipe hanging and that's not ideal (it will come apart at the clamps). There is no easy place to put hangers.

Now, before anyone jumps me, I have done all of this in the driveway while waiting for my 50 dollar cats to arrive and yes, I know my old cats were worth money but I wanted to know and now I do.

Finally, I took my entire pipe (prior to all of this experimentation) to a muffler shop that has been in business for 40 years. They quoted me 225 each for the cheapest cats they could find and said that the driver side pipe angles look crazy (they would have to do it on the truck to make sure everything fit).

So, this weekend, I am sure I will make ten trips to the parts store and hardware store for little bends and bits in order to put my extremely ugly welds on them and resolve my problems for good.

 

This may help you a bit.
Even though it was a 1997 D1.

http://jeffreyfall.com/landrover

 

Universal 2" cats from summit: $60ish each.

And 2 options:

Option A: $100 bill and a 6-pack of Fat Tire ale to the guys at the muffler shop at 3PM on a friday.

Option B: bust out the welder, keep the Benjamin (so the SWMBO can spend it), and drink the fat tire.

Pat your manly self on the back for solving the problem, welding, and drinking beer. Your SWMBO has $100, you're not being an arrogant, earth-raping american ***, and life is good.

 

option A , think of the time you will spend get all the rust and crap out of your eyes, ears and nose. Spend the hundred and sit back and drink bear.