LEXUS GS 400 98 to 2002 comes with 2 catalytic converters, like ours and inside they are made of metal not ceramic material,
i have them on mine they work wonderful, and u can find them very cheap since no one can recycle them as regular cat converters
and the size is also just like original land rover
Exhaust shops have "high performance" cats suitable for 5 liter V-8's that are quite small and only about $200 each installed. I had to put one on my Olds wagon (with a Rocket V-8) to pass smog seven years ago, and it worked great. Call around your town, and you'll soon learn what's available.
And, like the ccec writes, smile and write the check. But shop around first.
Oh, the emissions guys can use a non-contact pyrometer to check which cat is failing. A working cat will be much warmer than the incoming exhaust pipe temperature when it is after-burning. A bad cat will the the same temperature as the incoming exhaust stream or a little cooler. You may only need one cat. My wife's Rover had one cat (the cylindrical one on the left) that had disintegrated and melted, but the flat one on the right is still just fine.