A lot of unknowns regarding just how fit everyone is at the end of the season.
You can play Walker as a genuine interchange Hooker, in order to spell D Clark, or you can use J Clark or Ratchford in case of injury. Moving a player who's already done a lot of minutes up to Dummy Half doesn't give you that same injection of pace that you get from bringing a fresh pair of legs off the bench.
If everyone is as near fit as is possible this far in then I think that he'll start with J Clark at 13, Hill and Mulhern as starting props, Philbin and Akauola off the bench, Walker as interchange then it's between Longstaff and Austin for final place on the bench. I think that he'll stick with Thewlis on the wing despite Ashton's MotM performance last week.