Looks like this project has a bit of history. Personally I’d love the best possible open matte version. (Last seen on DVD?) There are too many shots where the framing is composed for 1.33 to say that 1.85, 1.78, or even 1.66 is appropriate. Kubrick obviously intended this movie to have a future outside the theater, i.e. on 4x3 home televisions.
Anecdotally this is because he saw 2001 on TV once and was dismayed how it was horribly cropped. “I’ll make my new movies with future-proof tv format in mind,” he said to himself. I have no idea how I remember this tidbit and it could be entirely false, but it would make sense.