36-bit was a common enough word length. Not just UNIVAC, but IBM 360, PDP-6/PDP-10, and some others. Convenient both for octal (multiple of 3 bits) and working with pre-ASCII, 6-bit character encodings (multiple of 6 bits).

Which is why we have UTF-9 and UTF-18, as defined in RFC 4042.

https://datatracker.ietf.org/doc/html/rfc4042

(Spoiler: It's an April Fool's joke.)

I was coming to mention this, though I think my memory goes back to some LISP machine (and was related to car/cdr and related encoding if I'm not mistaken)

I went way down the rabbit hole on this one. Seems that they are still made and used, fascinating!