Hi what diameter is the exhaust tubing beyond cat.....

A vernier caliper is your friend.

Hi .... I know this, I actually have a TD4 ..... yes I know the exhaust is different.....
If diameters are the same (or close)..... I was considering using the L series inter pipe to connect to a new std silencer.......(this combo is very cheap) then weld up a cat bypass. This would enable me to keep my old TD4 system(and very expensive inter pipe) in case I wish to revert.......