I actually don't believe any parts are interchangeable between the Franchi and the Benelli. Benelli would be stupid to allow that IMHO. But pull the innards out of each gun and you can see the distinct similarities, workmanship, fit and finish. The way Franchi is keeping the price down is limiting the number of models and options.
I own both Benelli and Franchi, time will tell if the Franchi stays in the same lane. One big plus for the Franchi is the bumper to bumper 7 year warranty. Benelli is only 1 year. We shall see.
Sometimes wrong, but never in doubt...