Maybe this is splitting hairs, but ...
First, consider whether your Benelli is a pre-ban or post ban. A PISTOL GRIP post-ban cannot have a mag extension holding more than 5 (?) rounds. Post-ban, no pistol grip, you can have a full length (7? 8?) mag extension.
Second, the M1 rear sights have been changed twice (meaning 3 different sets). The original issue did NOT have the windage adjustment on the right side of the dog ears. More importantly, it used small (~ 2mm) set screws, which sheared when you fired heavy loads (it happened to me, thank goodness for the smart guys at Brownells who fixed me up w/ replacements). Benelli then upgraded to larger (either 2.5 or 3 mm) set screws. It must have still had problems, b/c the final / current rear sights have the side adjustment as mentioned before.
There may be other differences still, but the above I can vouch for.