In his editing for the 1837 edition, Joseph Smith first thought to move the preposition of from the head of the relative clause to the end, but then he changed his mind. Elsewhere, when the verb of the relative clause is speak, the text overwhelmingly prefers having the of at the head of the relative clause: out of 52 clear cases without any textual variation, 46 have of at the head, 6 at the end. For a complete list of the examples involving speak (including four unclear cases with variation), see relative clause in volume 3.
Summary: Usage elsewhere strongly supports the placement of the preposition of at the head of the relative clause, especially when the verb is speak.