I find O Callaghan very interesting in that he doesn't seem to do a lot of hurling in a game, but usually his man does a lot less, which is the point of a full back. But, I think he has limitations to his game, where O Donnell has very few. But it might be a case that O Donnell can handle the corner position better then O Callaghan, so it would be better with O Callaghan at 3 and O Donnell at 2.
On Tayto's post above, I think the full forward line is our weakest, so I would put Shutte in there to shore it up a bit. I would have Treacy in the middle of the field, he doesn't win enough ball to take up a forward position, but is still worth having on the field. He is worth a point or two extra on the frees then Burke (although Burkes day will obviously come on the frees). Barrett, Boland etc. also options. Boland was one of the best U21s in the country two years ago, injury seems to have hampered him a bit, but there is no reason he can't be a star in the future.