The 1849 LDS edition removed the perfective auxiliary had here in 3 Nephi 18:8. This change appears to be accidental since in narratives the text otherwise has examples of only “when X had said” (36 times). There are no examples in Book of Mormon narratives of “when X said”. There are, it should be pointed out, two examples without the had, but these do not occur in narratives:
In these two cases, the use of the said without the perfect had is appropriate. The critical text will restore the original “when he had said these words” here in 3 Nephi 18:8, thus making the usage consistent in all narrative passages.
Summary: Restore the original text in 3 Nephi 18:8 (“when he had said these words”) since Book of Mormon narratives consistently use the past-perfect auxiliary had with said in when- clauses.