For what it's worth, when I had my cats fitted, my local MD did it and did a fine job. The car had just turned 7 years old and 50k miles at the time and everything came off pretty easily.
They used some new U clamps which they had to source from elsewhere as the Maserati ones only come as a part of the centre section fitting kit. The existing cats are much heavier than the Larinis (or any after market option I would imagine) and the new cats did not require the dual hanging support bracket so this was not used. They also had to slightly re-shape a heat shield section so there was no rattle once it was fitted.
It all went well however and all in, took around 2 & half hours for the X-pipe and cats.
When you come to do this, I would be more than happy to meet up where there's a ramp so you can have a poke around under mine to see how they were fitted if this helps, just let me know.