It willlook like 3 at the back, but Stones will play across the front of the back two of Kompany (or possibly Laporte, if Pep thinks two games in 5 Days is too much for Vinny) and Otamendi.
It looked like Pep briefed Stones on that very thing when Ferna got the hammy, but the shuffle worked and he didn’t use him.
I’d play the exact same team, but with Stones in Ferna’s place, alongside Gundogan, and awe drown in goal. That would also allow Ilkay to get forward and increase our height defensively and on the attack