Musica Sacra, the website of the Church Music Association of America, offers ICEL’s English missal chants in 4-line square-note Gregorian notation for the Order of Mass.
ICEL itself offers these chants along with all the other English chants (prefaces, antiphons for particular days, etc.) at its website. ICEL provided the chants to the English-speaking bishops’ conferences in 5-line notation. ICEL considered offering both 4-line and 5-line, and even planned on that for a time. Then it was decided that this would be a waste of ICEL time and resources, since no conference would elect to publish 4-line chant in its liturgical books anyway.
Then the question arose: What about folks who want to publish the missal chants in 4-line in their own publications? Would that be permitted, though it’s not the ‘approved’ ICEL notation? Yes, the thought was, there’s no reason not to allow that. And if some want to add in episemas, it’d be hard to disallow that, since the Holy See allowed the Solesmes monks to add in their rhythmic signs to the Vatican edition back in 1908.
The CMAA 4-line looks very attractive to my eye. No episemas, BTW. Enjoy.