No offense but 3 at the back will never work, especailly if one is a LWB, essentially it should consist of 3 CB's and if Grosso was going to play anywhere it would be wiser to play him on the left midfield birth so he can switch between a LB and stampeding forward.
Also Chiellini's madness moments would seem 10 times worse if he's in a 3 man defence, even 2 man in which grosso is absent.
Call me crazy but the best line up for that formation would be.
Buffon
grygera canna chiellini
camo melo momo grosso
Diego
Trez Iaquinta/Amauri
which if you think about is kind of what we play anyway as Grosso is usually so advanced forward.