750th post here, so some history seems appropriate.
As it currently stands, over a hundred episodes of black and white Doctor Who are missing from the archives, and many are likely to remain so short of a strange man in a police box intervening. These include nine complete stories, starting with Marco Polo, and including the Second Doctor’s first full adventure, Power Of The Daleks. There are clips and pictures here and there, and unofficial audio recordings of whole lost stories, so they aren’t as lost as some famously lost works of art, but still.
So there’s room to pick them up and remake them... perhaps as adventures. They’re included in the Doctor sourcebooks, so some of the pieces are already there.
I’d be tempted to revise and modernise as well:
Marco Polo presents the historical character as an adventurous explorer, but consider a version based on the idea that he was a fraud adapting other travellers’ tales - or a Pseudohistorical adventure that runs with the idea that he passed on stories of dog-headed people and other non-human species.
And Power Of The Daleks is the archetype for the “monsters acting nice” story type, which the Daleks pull fairly often among others. For one example, they tried it on Churchill...