Anyone know the stock exhaust size at this section?

[dools225]

Hi all, hoping someone can help me with this info. Will soon be fitting my R32 rear valance, and as such modifying the exhaust to exit centrally. Does anybody know the size of the exhaust as it enters the backbox? Need O.D and I.D. This is so I can prepare my joining piece before hacking it up, need to do it in one hit as my car is used daily.

Thanks in advance