Fiat like to use what's in the parts bin and in my experience most are interchangeable.For a short period of time the did a version with a centre box and rear pipe. Not sure why unless this was due to supply issues. I’d be almost certain they are interchangeable. The catalytic converter flange has not changed so you would be able use a middle pipe and back box. Just be aware of cheap copies that are inferior to the originals. I managed to source a good second hand mid pipe and back box off a car that had done 19k for £60