Not sure if this helps, but here goes...
Bosal list the same exhaust part numbers for the 147 1.6 TS and the 2.0 TS centre section and rear silencer,meaning the exhaust diameters are the same size. Both are listed with a silenced centre section though.
Interestingly, the 147 1.9 JTD has a non-silenced centre section, but the JTD rear silencer has a different part number to the petrol version, which means the rear box is either a different pipe diameter or the internals are different (or both).
What may be of some use from the information is, if someone can measure the outer diameter of their JTD exhaust pipe and you measure yours. If the JTD and Petrol sizes both match, you could use a JTD centre section with your OEM rear box and save a fortune on a supersprint alternative.
The reason i mention all this is the 156 2.5 V6 has the same outer diameter size as the 2.4 JTD. This may
be similar with the 1.9 JTD and 2.0 TS.