When we played 4-3-3 in that season our LBs were for the most part Chiellini or De Ceglie. I remember Grosso playing one game in that position against Siena when both of those were unavailable
back then we did not have Vidal though!
The first part of 2011, i missed it, due to my time in the army, we have used Chiello as LB.
This is when the hybrid 4-3-3 was used, hybrid because Pepe was more of a LM, starting from the middle of the field, rather than out of the box, towards it.
Conte and vidal both came at summer 2011. Because we had a terrible defense up untill then, Conte was forced to use a second wall of defenders, so he immediately switched to 3-5-2.
Ever since we have yet to try the 4-3-3. It is important that we never really did try the 4-3-3 with the great midfielders we have today and with 2 SSs upfront, behind a real CF
This could be far more efficient that it once was, the reasons why that 4-3-3 has failed then was because of material.
This material could have done a lot better and i believe that it is unfair to consider the 4-3-3 as a failure because of the material we have had back then...
At any case, conisering our material now, i think that we should also try the 3-4-3, with the middle line being a diamond with Pirlo playing deep, 2 CMs besides and one closer to the forwards/
The forwards being 2 SSs, of the many we have, playing wide and force the opposition defense to cover the full lenght of the stadium and one CF up front, that is assisted by the front midfielder and the 2 SSs