I wouldn't want to make too many changes to the World Cup team as I'm not sure many if a lot of the 'new' players mentioned here could come in and improve the team. The only change I would make that wouldn't be enforced would be Shenton over Cudjoe.
Clark will probably get a run from the bench and you can't argue against that on form, his stats are quite amazing in terms of tackle busts and average gain considering he plays through the middle. From what I've seen of him he thrives on a quick ruck which he won't get as often in internationals so it will be interesting to see how he goes.
Replacing Sam Burgess is the impossible task.