I have always thought that the casting in this film was brilliant. Scatman Crothers did work with Jack Nicholson in four films, he did a bit of TV, but acting was a side gig for him, not his bread and butter. He has just a bit part in The Shining, is unknown to most of us and is freed from transference by us of other roles he's played. Under Kubrick's direction, he plays this bit part superbly.
Barry Nelson is another. Perfectly cast as the face of the Overlook Hotel. You don't expect B-level actors to turn up in Stanley Kubrick films.
The same with Anne Jackson--whoever she was! She is perfectly cast as the matronly doctor who makes a house call when Danny has his first "shining" about the Overlook Hotel, an epileptic-like seizure that Jackson terms "autohypnosis". Her subtle acting here is perfect.