As Kristian has said we both use same model, but no matter which one you use you are going to have to either modify your existing exhaust or get e new bespoke one made which i would recommend as even an aftermarket performance exhaust is going to be restrictive as its made for a 1.1L engine, not a 1.4L.
The standard system as fitted to the Stilo our engine came from was bigger in diameter than the SuperSprint system we had on Emma's Cinq.
And the system fitted to Emma's Dad's 500 1.4L is fairly big as well.
Another consideration is CAT placement if you are keeping it, we did to ensure legality in case of VOSA road side random checks and ease of MOT's, on the MPi Seicento the CAT is built into manifold as it is on all modern cars to heat it up quicker making it work earlier and therefore be more efficient. Fortunately as the floorpan is same as older Spi models & there is the lump in floor pan for the CAT to sit which is where ours went. Plus modern CATS are not as restrictive as many think they are.
Good luck with the conversion.
The standard system as fitted to the Stilo our engine came from was bigger in diameter than the SuperSprint system we had on Emma's Cinq.
And the system fitted to Emma's Dad's 500 1.4L is fairly big as well.
Another consideration is CAT placement if you are keeping it, we did to ensure legality in case of VOSA road side random checks and ease of MOT's, on the MPi Seicento the CAT is built into manifold as it is on all modern cars to heat it up quicker making it work earlier and therefore be more efficient. Fortunately as the floorpan is same as older Spi models & there is the lump in floor pan for the CAT to sit which is where ours went. Plus modern CATS are not as restrictive as many think they are.
Good luck with the conversion.