The original manuscript is not extant for the word into in the phrase “their journeyings into the land of Nephi”, but spacing between existing fragments indicates a better fit if the original manuscript read into, though the shorter in is still possible. In any event, 𝓟 reads into, which the 1830 compositor set as in, perhaps because of the in in the immediately following “their sufferings in the land” (for discussion regarding accidental mix-ups of into and in, see under 1 Nephi 4:33). But here in Alma 28:8, the compositor may have also been influenced by the oddness of the phraseology “their journeyings”, which sounds like a continuing action and more than one journey. In fact, the use of into would work better for modern readers if the text had read in the singular and as journey (thus “their journey into the land of Nephi”).
The account of the missionary labors of the sons of king Mosiah includes both their journey into the land of Nephi as well as their journeys throughout that land. Moreover, there are clear examples in the Book of Mormon text where journeyings is actually used to refer to what modernday English speakers would consider a single journey:
The first example deals with the journey of Lehi and his people. The second and third ones refer to the journey the sons of king Mosiah and their missionary companions made to the land of Nephi. The description in Alma 17:5–13 seems to restrict itself to the journey prior to arrival in the land of the Lamanites. There is no mention in this passage of Ammon and his brethren being persecuted or suffering at the hands of the Lamanites and the Nephite dissenters (as there is in Alma 26:28–29); instead, the passage in Alma 17 mentions the difficulties of only the journey in the wilderness while traveling towards the land of Nephi. When these missionaries finally split up, the text does refer to “their several journeys throughout the land” (Alma 17:18), but note here that the word is journeys and not journeyings.
We should also recognize that this passage in Alma 28:8 gives a chronological listing of what Ammon and his brethren went through on their mission: first their journey to the land of Nephi, then their difficulties (sufferings, sorrows, and afflictions) in the land of Nephi followed by their great joy when the Anti-Nephi-Lehies converted, and finally the Nephites’ acceptance of these Lamanite converts. The journey into the land of Nephi was a very difficult one for the sons of Mosiah; in fact, they almost turned back: “now when our hearts were depressed and we were about to turn back / behold the Lord comforted us” (Alma 26:27). So it is not surprising that the first stage of their missionary work was included in the listing in Alma 28:8. And thus the use of the preposition into is perfectly correct in Alma 28:8 and will be restored in the critical text.
Summary: Restore in Alma 28:8 the preposition into, the reading in 𝓟 (“their journeyings into the land of Nephi”); the plural journeyings is used elsewhere to refer to this difficult first stage in their mission (Alma 17:5–6); because Alma 28:8 is a chronological listing of the different stages of this mission to the Lamanites, “their journeyings into the land of Nephi” is appropriate.