Unless Williams is 100% I wouldn't be playing him, last time he played with a niggle it was aggravated and he was set back a few weeks, Ratchford & Hayes are fine at half back. Drinkwater shouldn't come back in fit or not.
4th Prop / back row is where the biggest question marks lie I think, I'd like Holroyd to keep his place, I'd be tempted to put Crowther & Nicholson on the bench and give Phlbin the week off, he's placed some decent minutes over the past few weeks, but Catalan are a big old team, we need some size out there.
Dufty
Thewlis
Tai
King
Ashton
Ratchford
Hayes
Harrison
Walker
Vaughan
Fitzgibbon
Holroyd
Currie
Powell
Musgrove
Crowther
Nicholson
Left out Williams, Drinkwater, Whitehead, Philbin
however I have a sneaky suspicion Holroyd will drop out and Nicholson will move up in to the starting 13 with Philbin on the bench. (I'd like to see Currie stay at 13 though.....)