I've asked this question in /r/AcademicBiblical, but without response.

According to my rather limited reading, Jewish Eschatology apparently involves the "four craftsmen" - Elijah, Messiah ben David, Messiah ben Joseph, and the Righteous Priest. There are two messiahs, but if one is referred to without qualification, the reference is to the Messiah ben David.

In the NT, some of this can be seen. John the Baptist is associated with Elijah, and in the Palm Sunday narrative there is a clear echo of the Messiah ben David. Arguably the Messiah ben Joseph may be referred to in "destroy this temple, and I will rebuild it in three days", as one of the roles ascribed to him is rebuilding the temple (usually assumed to be literal rather than figurative).

As far as I understand, Elijah, the Messiah ben David and the Messiah ben Yoseph were already part of Jewish eschatology at the time of Christ. However I'm interested in the fourth, the Righteous Priest. Currently this person is associated with Melchizedek, but I have not been able to find out how long this has been the case. I'm particularly interested in whether this would have been true when the Epistle to the Hebrews was written, probably about 63-64AD.