The original manuscript is only partially extant here, but it is clear that in writing down Joseph Smith’s dictation, Oliver Cowdery originally wrote some other word after “he spake of”, crossed it out, and then supralinearly inserted Hell. One possibility is that the initial word was eternity—that is, Oliver started to write “and he spake of eternity”, thus initially omitting the first prepositional conjunct (“of hell”). In any event, there is no reason to reject the earliest extant reading “he spake of hell” (the corrected reading in 𝓞).
Summary: Maintain the earliest extant reading for Jacob 7:18 (“and he spake of hell and of eternity and of eternal punishment”).