I would've taken Dubinsky and Ryan ahead of Stepan and Callahan.
--Dubinsky would be the 5th center and between him and Oshie one of them can slot in next to Backes, the other being the scratch.
--Ryan can be the #13. They can plug him into any line they want if they need the goals. An offensive specialist if you will. You don't need to give him a regular shift (unless he earns it, which is also a real possibility)
This isn't as much a shot at Callahan as a realization that if you want to have that option of Bobby Ryan available, you need to add that 5th center, and Dubinsky is as good as you're going to get to a center version of Callahan (who can also play wing).
But it is what it is. The more I think about this team, the less sure I feel about anything. Does it have enough speed? Enough offense? Enough size? The reality is the team is extremely well balanced--not truly elite in any one area (other than goaltending), but good across the board. I feel like this is a team that can adapt and play different styles, which could turn out to be really important based on the opposition.