Here the 1874 RLDS edition omitted the preposition unto. This appears to be a typo since most other instances of “like unto X” were left unchanged in the typesetting for the 1874 edition. Nonetheless, there was some tendency for that typesetter to omit the unto in “like unto X”. For two other cases, see under Alma 26:27 and 3 Nephi 20:7. Here in 3 Nephi 29:7, as in the two other cases, the 1908 RLDS edition restored the preposition unto.
Summary: Maintain in 3 Nephi 29:7 the use of unto in the phrase “like unto the son of perdition”, the reading of the earliest textual sources.