Although the form of this beth differs from the beth in the first word of the inscription, the difference is not significant. Over 20 years ago, Nahman Avigad noted that the use of different forms of the same letter in the same inscription, sometimes even in the same word, occurs very frequently in monumental and ossuary inscriptions (“The Paleography of the Dead Sea Scrolls and Related Documents,” in Aspects of the Dead Sea Scrolls, Scripta Hierosolymitana IV [Jerusalem, 1958], pp. 56–87). Many of the ossuaries to which Avigad refers present two forms for beth: the common one, with a long base line extending to the right of the vertical, and a form with a truncated base line perpendicular to the vertical line. I believe that both forms of beth are represented in the Temple Mount inscription.

See also the Uzziah inscriptions in Inscriptions Reveal (Israel Museum #255, 1972), for two forms of he and mem.