My Rock and my salvation, 4: the Targums

I am still puzzling over the Septuagint (LXX) translators' reluctance to translate the rock metaphors from Hebrew into Greek, substituting for them such words rendered in English as strength and helper. This metaphor is also absent from the Latin Vulgate and, with one exception, from Miles Coverdale's Psalter in the Book of Common Prayer. It occurred to me that perhaps the LXX translators had access to a lost Hebrew manuscript that had already made these substitutions. But there's another possibility.

After the Babylonian exile, Jews ceased to pronounce the divine name, יהוה, often rendered YHWH in the roman alphabet. When they came to this name in the biblical text while reading, they would orally substitute אֲדֹנָי‎, (Adonai) or LORD. Accordingly, the LXX translated the divine name with the Greek word Κύριος (Kyrios).

This prompts me to wonder: what if the returning exiles were also reluctant to employ the rock metaphor for God and, when seeing it in the text, substituted another word as they read aloud? I floated this idea with my good friend and biblical scholar, Al Wolters, and he suggested that I look at the Targums, which represent a codification of oral readings of the Scriptures translated into Aramaic. Indeed an English translation of one of the Psalm targums is found online: Targum Psalms: An English Translation by Edward M. Cook. Sure enough, in only one place is the rock metaphor for God found—in Psalm 71:3:

Be a strong mighty rock for me always to come to; you have given commandment to redeem me, for you are my strength and my stout fortress.

Oddly enough, the second occurrence in this verse of rock in Hebrew is replaced by strength in this targum. All other references to God as rock have been changed to substitutes. This suggests to me that the LXX's seemingly faulty translation may have its origins within already established Jewish liturgical usage of the era. Did the metaphor seem to put God on the same level as natural phenomena? Were there people who used stone structures to represent God much as Jeroboam sought to represent YHWH with the two golden calves at Bethel and Dan (1 Kings 12:25-33)?

I am not a biblical scholar, of course, and it's possible that someone better versed than I in the field has written about all this somewhere. If not, it might make a good dissertation topic for a graduate student in the discipline.