Thank you for your reply.
In France the particle filter on the 320d is not the default option and the dealer are advising not to take it... Actually it is to late now to change this option on my car as i will receive it in one week.
Because of the downturned part I think I will have to cut the end of the exhaust and then put an chrome tip on it (I would like a dual exit one).
Still I would appreciate a lot that someone give me the diameter of the pipe on the 320d.
This diameter/size would probably have to be measured a bit before the end of the pipe were it becomes an oval (as you can see on 320d picture with particle filter I have found on the internet).
Thank you.