Once more we have an example where these and those have been switched in the history of the text; for a nearby example of the opposite change, see under verse 16. Here in verse 20, Oliver Cowdery changed these to those when he copied the text from 𝓞 into 𝓟. In this letter of Helaman’s, we have two other examples of these or those occurring with two thousand:
Either reading is theoretically possible in Alma 57:20, so the best solution is to follow the earliest textual sources (in this case the original manuscript). For further discussion of mix-ups between these and those, see under Alma 3:25.
Summary: In accord with the reading of the original manuscript, restore these in Alma 57:20: “these two thousand and sixty”.