I too looked up some minor translations for clues, such as Rotherham and Goodspeed, but nothing doing.
Except that the rendering of Rotherham in Psalm 68:18 uses the "consisting of men" phrase.
Thou hast ascended on high, Thou hast led in procession a body of captives, Thou hast received gifts consisting of men, Yea even the rebellious, That, Yah, Elohim, might settle down to rest.
And we know Rotherham was a very influential translation for early Bible Students and for Franz when translating the NWT. The Catholic Douay version has similar.
Franz was fond interpreting the Greek in light of his understanding of the Hebrew in quotations. His attitude seems to be that his reading of the Hebrew original should be determinative of the meaning of the Greek as much as the grammar and context of the Greek itself. He argued for his translation of Heb 1:8 partly on the basis of the Hebrew construction in the Psalm. And of course, most famously, Franz argued that the presence of the divine name in the Hebrew of verses quoted in the NT warranted the inclusion of the divine name in the NT translation.
The best place to look for clues why Franz chose this peculiar translation for Ephesians 4:8 would probably be a close examination of how the verse is discussed in the Watchotwer and Awake! articles of the 1940s and 50s. Franz elaborated many of his ideas about translation in this period in study articles, questions from readers and other pieces.