You're overdue for all for O2 sensors at 200k miles.
Cat's are integrated into the manifolds. Not too hard to replace (rust notwithstanding). They can be finessed in and out without moving the engine or anything important.
If you can get cat's... send me a set. In the states scrap cat's are valuable enough that even whole junk cars usually have them stripped off before you get your hands on it... and it's basically illegal to resell salvaged ones.
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Sometimes a bolt is just a bolt.
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