We sang that antiphon in English until recently, pretty much as you give it, but with two differences: name (c-a) of (b) the (a-b) Lord (g), and O (c) King (c) of (c) Is- (c-c-c). This is pretty much the version in the Wantage gradual. I am sympathetic to their aim to keep the melody intact as much as possible, but instances in the Latin repertory itself, where the same melody is used for more than one text, show that in the case of more syllables, additional notes of recitation are added, rather than breaking up a neume. Thus, O King of Israel: has three more syllables than the Latin, but in the Latin the accented syllable of Israel, the most important syllable of the phrase receives the tristropha, best kept as the three c's, preceded by recitation on c for the three syllables before it. On the other hand, "Domini" in the Latin version of the melody has recitation to accommodate the fact that the accented syllable is the ante-penultimate syllable, while "Lord" is an end accented syllable and best suits the single note. "

The reason to make such adjustments is that the accent of the text differs, and the melodies do take that into account.

The process differs for each genre of chant, since for each genre, there is a different relation between text-accent and melody. I found that the Wantage melodies were quite satisfactory in the melodies at the level of psalm antiphon, as this one is, and particularly the antiphons for the Maundy on Holy Thursday, perhaps because they are melody-types and sometimes actually set a dozen or more texts throughout the repertory; the more melismatic the genre, though, the less satisfactory the literal setting the the Latin melody becomes.

Thanks, Francis! I saved a copy for next year.