There are two variants here involving the word of. In the printer’s manuscript, Oliver Cowdery initially wrote “of the land of the city of Zarahemla”, an obvious error since only the city was in the hands of these rebels: “they do fear us and durst not come out against us to battle” (verse 7) and “he hath agreed to maintain the city of Zarahemla” (later in verse 8). Oliver probably expected “of the land of Zarahemla”. Later, possibly when he proofed 𝓟 against 𝓞, he crossed out the of and supralinearly inserted the or (the level of ink flow is somewhat heavier). The critical text will, of course, maintain the corrective or.
The second variant deals with the loss in the 1840 edition of the preposition of in “the city of Zarahemla”. The omission was not the result of Joseph Smith’s editing for that edition; other instances of the of in that phrase have been left unchanged in the 1840 edition, including one more in this same verse: “he hath agreed to maintain the city of Zarahemla”. Besides these two examples, there are 14 examples of the specific phrase “the city of Zarahemla” in the original text but none of “the city Zarahemla”. In one of these other examples, the of was omitted in more than one edition (as well as initially in 𝓟):
Here the 1841 British edition and independently the 1902 LDS missionary edition omitted the of. It is also probable that the 1905 LDS missionary edition omitted the of here without reference to the 1902 edition since the copytext for the 1905 edition was the 1879 LDS edition.
So the text is fully systematic for the specific phrase “the city of Zarahemla”—the of always occurs. But there is variation for the occurrence of the of when great occurs in this phrase. When the determiner is this, we get the of, although there is only one occurrence of “this great city of Zarahemla” (in Helaman 13:12). On the other hand, when the determiner is that, the of is consistently lacking, thus “that great city Zarahemla” (in Helaman 1:18, 3 Nephi 8:24, 3 Nephi 9:3, and 4 Nephi 1:8). Thus there is some systematicity here, but ultimately the critical text will in each case determine whether the of occurs in the phrase “city (of ) X” on the basis of the earliest textual sources, as explained under 1 Nephi 11:13 for the phrase “city (of ) Jerusalem”.
Here in Alma 61:8, the of in “the city of Zarahemla” was restored to the RLDS text in the second edition (1892), which is rather surprising since that edition closely follows the first RLDS edition (1874), being set from that edition without hardly any intentional substantive changes. Perhaps the restoration of the of in the 1892 edition was simply an accident.
Summary: Maintain in Alma 61:8 the of in “the city of Zarahemla”, the reading of the earliest textual sources; also maintain the corrective or in “the land or the city of Zarahemla”.