Sorry there is some confusion. I'm not talking about CB's playing FB at all, of which I'm not really a fan. As for a CB playing WB, not a chance, I don't know where this has come from in your post.
I'm saying Barzagli plays in a back three and has none of the physical attributes you say is essential to the role, he is a classic CB. He plays very well there by all accounts. You could argue Serie A doesn't have the abundance of pace that the PL does, and this weakness of Barzagli's would be exposed here, but I think this is a moot point as I've explained earlier.
BTW I'm arguing all this but I think we should go to a back four as soon as Dunne gets back. Nothing to do with Baker, I think Bennett and Lowton aren't up to the job of playing WB, not yet at least.