When Llewyn checks out his and Mike's record, "If We Had Wings" in the Gorfein's apartment in the beginning of the film, the bio underneath Mike Timlin's name is word-for-word that of Dave Van Ronk.
The character Troy Nelson is based on singer-songwriter Tom Paxton, who served in the army before beginning his career in Greenwich Village. Paxton's song "The Last Thing On My Mind" is featured in the film, and the Nelson character makes an implicit reference to another Paxton song "Buy a Gun For Your Son."
Not only does the cover of the "Timlin and Davis" album shown near the beginning of the film recall the cover of "Inside Dave Van Ronk"; we can see that the liner notes are about Van Ronk.
During the scene in Washington Square park, the new stone benches that were added to the park in the recent renovation are clearly visible in the background.
It was Elizabeth (Betty) Hobby's husband. (She was the singer from Arkansas who Llewyn berated when he was drunk the previous night). The last thing he says as he walks out of the alley is My wife up there trying to sing.'