With a car like this, there is a lot to be gained by using some of your own time to work through and check various items just to give you a baseline to move forwards.
If it was mine, I would renew the air filters, clean and then check the MAF, check the readings from the inlet air and coolant temp sensors, clean the throttle plate and bore, check all the vacuum connections and inlet gasket points for leaks, check EGR and EVAP systems are working and clear, check plugs/caps/leads (you already have), check for exhaust manifold and pipe leaks and change the engine oil and filter.
Then check/get checked the injector health/adaption/O2 sensor readings to verify all is well "upstream", clear the codes and then see if you need the CATs (at least they will then be protected).
Not much cost in parts - mainly time - and you will then be sure of the basics.
(A quick search shows that the aftermarket exhausts that remove the CATs are used to replace the rear ones and to scare the living cr@p out of old ladies as you cruise past. Who knows if the car can still pass an MOT afterwards?).
I have no details on your model, but usually the makeup of reduction and oxidation material in CATs designed to be used in sequential pairs is different - they are used to clean up different pollutants and designed to work together.
All the codes are telling you is the level of O2 in the stream before and after the front cats was similar at the time the code was set - the fact you had quite a long drive time before the light came on means there is still hope for them...there is, however, a good chance that the misfire history has done some damage as the unburned fuel from the misfire could have overheated them.
What's the mileage (and is it verified genuine)?
I have booked it into MB Tech in Warrington for the 6th July. Fingers crossed it wont be the Cats......
I have just had a price of £1284 delivered, with 2 year guarantee.
