Hyphens, En Dashes, Em Dashes

Q. Should a range of specific dates be written using an unspaced en dash, even in headings? Which is correct: 14 March 1879–8 April 1955 or 14 March 1879—8 April 1955?

A. The first is Chicago style (please see CMOS 6.78), but changing the dash to “to” will make the phrase more readable.

[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]