Everyone.
Seriously though... we've had some time to see this question answered.
For McInnes coming off the bench the last little while, the strategy has been for him to either play the final 60, or for him to play about 40-50 and then bring on someone else to finish the game.
I don't think there is much difference between 8, 10 and 13 with the ball for the Sharks atm. I think Fitz wants one big bloke on there at all times for kick returns and to take the "pre-shift" or "pre-clearing kick" hit up, but the other 2 could come from blokes under 105kg and he'd be comfortable playing like that for 15-20. I don't really see much of a difference in ball movement between forwards other than to say that Finucane is better than the rest. Even some of BHU early-season games you could look at and say that he is playing like a 13.
Defensively though, McInnes is a wolverine and covers a lot more ground than the bigger blokes.