make the cut as close to the back box as posible this will leave you about an inch after the braket to atache a new pipe. if you know someone doing a de cat there is a bend on that pipe thats perfect for a side exit. it just sits over the inch of pipe you have left and just clamp it up.
I would advise a bit of cheq plate on that back wing just for some extra suport and to help stop the vibration
i will have a look see if i have some pics
stretchy