XJR Catalytic Converter Question/Advice

[Lordgaz]

I'm jumping the gun a little here as the car is in the garage being diagnosed, but this post is following on from this one here:viewtopic.php?f=281&t=13971

Car was lacking power when throttled, and also had some pinking style noises coming from somewhere + a rattle under the drivers floor plan - Engine seemed also to get "ticking" hot on one side (though water temperature was showing on the dash as fine)

There are several causes I guess, but I am pinning this on a blocked or collapsed Cat at the moment - (When I went to buy the car with a friend, I have a recollection of the seller saying something to him while I was inside the car about a blocked Cat then, and it being fixed - though no more of it) - but maybe the Cat was bodged or swapped for something on its last legs) -

Question is - Can Cats
A - be rebuilt
B - anyone have any experience of Magnaflow cats
C - anyone know someone to talk to about aftermarket or 2nd hand cats

Cheers
Gaz