Does the written story itself also read explicitly as a nod to M.R. James? It certainly feels like it must from both of our descriptions of the film.

It feels so entirely like Aickman as a story, it's hard for me to tell! I was surprised by the fidelity of the adaptation. There's one scene in the short film that doesn't appear in the story and vice versa and otherwise even almost all of the dialogue is the same. The Latin was invented for the film—John Trant, the traveler in the story, is looking at an inscription when the stone door opens, but we are not told what it is.