Shinnie is the power and legs in the middle, have you not watched any of our games this season? There's absolutely no chance we'll dropping our captain for the biggest game of the season thankfully.
Duk at 10 is an interesting one. He's never played that say for us before (he's played in a front two, but never deliberately behind the striker), but I could imagine him just getting the ball and driving directly at them rather than any of that passing nonsense. It would be entertaining, as long as we didn't require any additional defending.
As most others have said, Shinnie forward in place of Clarkson would make most sense against the Tims. Shinnie to get right in the face of McGregor would be interesting, see if he can get him booked early doors (Duk to come on and get him sent off!). Closing off that link between defence and midfield will be vital.
A toss up between keeping everything else the same and having Duk on from the start. Personally, I'd keep Duk on the bench, because of the discipline we'll need to have in shape. Duk was immense when he comes on, playing out wide, but there's no way we could have Duk out wide against the Tims for ninety minutes and not give up several chances. If he was starting, then, you'd probably put him at number nine, and then you're sacrificing the ability to take him on later to terrorise the fullback. I think I'd be inclined to leave him on the bench, and him and Clarkson can come on when we're one up and looking to stretch the lead.