Garnett is too old to play the 3.
IMO, McDyess looked as good as ever last season. Sheed, on the other hand, looked pretty much finished as a top player. Him and Nesterovic can't defend the younger, mobile big men or the dribble penetration any more.
McDyess may be similar to Baby, but he's a much better rebounder and post player. Of course, we'd need someone else to defend the post. I think I know an excellent fit, but it's a long, long shot