Here the 1920 LDS edition removed the negative not, probably because it was viewed as being a double negative when combined with the following prepositional but, which like the conjunctive but has an implied negation. In two other places, the 1920 edition removed similar examples of not used with but:
This editing out of the not has occurred only in the LDS text; the RLDS text has retained the not. Obviously, the sense of “not ... but” being a double negative is not that strong.
There is also one example involving “not ... but” that has been retained in the text:
Consistency in usage suggests that Jacob 4:1 should be edited to “and I can write but a little of my words”). In any event, the critical text will maintain the original usage in all four of these examples. For a complete analysis of multiple negatives in the text, see negation in volume 3.
Summary: Maintain the use of “not … but” as it originally occurred in 1 Nephi 14:28, Jacob 4:1, Alma 58:5, and 3 Nephi 6:16; the supposedly ungrammatical nature of this construction is not particularly noticeable.