Power Flow in Scotland gave me a cat back system for £320, £300 for a back box seems a bit salty. My 190 ZTT was 60mm and getting a standard box was not possible at the time.
I tried guys universal one on my brother Punto, it work ok, and they do an MG on, if you don't fancy standard?
https://www.ebay.co.uk/itm/FREE-FLOW...EAAOSwg9dZzO20
Standard cheepy!
https://www.ebay.co.uk/itm/Rover-Mg-...EAAOSwstJZTD6q