For an overview of the development of the Hebrew scripts, see Joseph Naveh, Early History of the Alphabet: An Introduction to West Semintic Epigraphy and Paleography Jerusalem: Magness Press, 1982) and Mark McLean, “The Use and Development of Palaeo-Hebrew in the Hellenistic and Roman Periods” (dissertation, Harvard Univ., 1982). Naveh’s plate 14D shows a fragment of the Psalms Scroll written in square Hebrew, but with YHWH in paleo-Hebrew.