Here the object pronoun form him was replaced with the subject form he in the editing for the 1920 LDS edition. As discussed under 2 Nephi 1:27, the original text had quite a few cases where the subject complement took the object form. Some of these have been edited, but not all (for some of the exceptions, see under Mosiah 15:18). For a complete discussion, see under subject complement in volume 3. The critical text will maintain the object forms whenever they are supported by the earliest textual sources.
Summary: Restore in Mormon 8:16 the object pronoun form him, the reading of the earliest textual sources (thus “and blessed be him that shall bring this thing to light”).