Allan Green should only take a fight against Calzaghe if he is offered it (which would mean he gets a big payday and a beating). However, Green, on a head to head basis, probably isn't a top 10 super middleweight despite his RING ranking. So a Calzaghe fight will never happen and should never happen.
I would love to see Allen "I Robbed Emmett Linton at Gunpoint" Green in with Joe C. Afterward he can "apologize for impersonating a fighter!" Boo