Mekari is the swing tackle at both spots, per Harbaugh. So he's the LT if Stanley is out (which is what happened yesterday). Mustipher is the new C (filled in for Linderbaum yesterday as well).
I don't know who the backup Center is or if we even have one. Manning and Doss were the only other lineman I saw on the PS, and I don't believe either has any C experience. So assuming PS isn't an option, I would think its one of three options:
a) Cleveland or Sala
b) a street FA
c) Mekari goes from LT to Center, and then Faalele goes to LT. This seems unlikely to me, but I guess its possible.
Dobbins and Williams going to IR seems obvious. So there's two roster spots. Imagine those are taken by Mustipher and Gordon as full call-ups from PS.
No idea with Linderbaum. IR is four weeks of no practice, so my best guess is they won't go that route immediately, but its possible. Stanley should avoid IR I would think.