Planet of Giants ... Watched the as-aired version. I watched some of the reconstruction of episode 3, but was too tired to keep going. Quite a nice story, though some odd editing choices in that "final" combined episode.
I don't think I was aware of this at first. It was filmed as four episodes. Someone at the BBC decided three and four were too slow, and had those edited together as a single episode. That left a one-episode hole in the schedule that was later filled by the Dalek cutaway leading into Dalek Masterplan.
It ends up being similarly structured to the modern episodes.
It would have easily worked as an 11/Amy and Rory story I thought when I watched it.