Probably right sided at that. Even then we could still be a bit of a liability over on the left. Lindsay is raw and, just going on the 75 mins I've seen of him, Sinclair may be more of an attacking full back than a last line defender.
If Archie misses out on Wednesday night due to his knock or only plays a wee while I'd imagine we'll have a clearer idea about the level Lindsay and Sinclair are at just now. It would tho' throw up a bit of an imbalance if we had to get another left sided defender in.