I just had the passenger side cat replaced on my 1985 Range Rover. It is using the exhaust off my now defunct 1989 including the '89's transmission cross member. Anyway, I bought a Catco converter on eBay for $35 plus $15 shipping. It was the 2 1/4 model that the seller was offering and it fit, albeit, in a snug fashion. I had the whole thing done by a local exhaust specialist and it cost a $150 including the cat. The job was done so that if I choose to, I can remove the cat and install a short straight pipe after the truck passes emissions. I am so satisfied with the experience that I am buying another cat from the same eBay vendor and I'm having the driver's side done as well. Then, finally, this grey market Rover will be running as clean as I can get it.
Just go to eBay and do a search for Catco Converter and the vender I used will come up, click on the 2 1/4 converter and buy it. When you get it it may seem a little large but trust me, it will fit. Alternatively, Perone Ford of the Fl. Rovers club did something similar but he used the Catco 6905 model converter that he bought from Summit Racing for $55 plus shipping. Before I bought the model I used I checked and the dimensions were the same for the one I used as the one Perone used.
Good luck.