I can now confirm that the M Performance exhaust will fit OK to the 320i. I got mine finally fitted.
As mentioned before you will need the adapter (60,2mm to 75mm) so you can use the standard exhaust pipe as well as the M Sport diffuser. Diffuser is a straight fit.
The 320i does not however have the cablings for the exhaust flap/valve release so you will need to disable it. You can do the
DIY - Exhaust flap mod (Golf Tee) or just remove the whole thing. I ended up removing the electronics and welded the nut so that the flap is always open.
I am very satisfied with the results. With the stock exhaust I could barely here anything from the back but now there is a nice growl.
Some pictures attached.
__________________
2013 BMW F30
320i - M-Sport, Alpine White, M Sport suspension and brakes, Sport AT, VSS, PDC, Xenon, High-beam assistant, Harman/Kardon, Extended BT, Rims 403M (summer 19") and 397 (winter 18"), M Performance: Exhaust, Rear Bumper Diffuser, Carbon fiber mirror caps, Carbon fiber rear spoiler, Black kidney grilles, Floor mats. 3M Brushed Black Metallic vinyl wrap roof.