There are a couple interesting studies out there of the legends surrounding the Rechabites, a non-Levitical clan that managed to get themselves attached to the priesthood (maybe as "associate" priests who could perform some priestly duties, more probably just those normally associated with Levites who were not priests = singers, porters, etc.)
There is, of course, a Nazirite connection. Something like Rechabite lore could explain how James, a non-Levite person of Judean descent, who practiced a lifelong Nazirite vow, could be considered a "legitimate" priest. Remember who Hegesippus claims called out in alarm when James was being stoned? A Rechabite. I understand there is a connection between Rechabites and clothes cleaners (and the fuller's club). This is sometimes connected to the fact that, in the temple, if a priest, even the HP, should intentionally enter their holy place of duty in a defiled state, "their head is bashed in by clubs." Who yields them? Likely the Temple police. Were they Priests, Levites, or Rechabites? Now there is some light on the way James was "dispatched," by means of a fuller's club.
The original Rechabites may not even have been a Judean clan, and certainly not Levites. I forget what they did for the priesthood, but whatever it was it so benefited them that the temple authorities made them honorary priests. I have heard it speculated (Schonfield? Eisler?) that Rechabites were not defined so much by family as because of their severe ascetic lifestyle, meaning "anyone" could become one by adopting their ways and in time be accepted as honorary priests.
There is a brief mention of them on page 347 of G R S Mead's Did Jesus Live 100 BC? (1901? 1903?). This is available online and circulating copies are available in most public libraries.
Robert Eisler goes into some detail describing where he thinks "Rekhabites" originated from and about what they are said to have done, in Messiah Jesus & John the Baptist
(1931), pages 234 sq., 238, 245, 276, 305, 322 sq., 328, 334, 343, 357, 360, 362, 366, 377, 416, 422, 430, 482, 497 sq., 519, 538, 541, 566, 573 sq. (so in other words "a lot"). This is available online (see the recommended reading section of this forum), but forget about finding a circulating copy at your local library, no matter how big. I managed (made them Cleveland Public Library dig it out of non-circulating storage), but just barely.
* There is a relatively recent (1985) translation of the Syriac version of "The History of the Rechabites," by J H Charlesworth, in The Old Testament Pseudepigrapha
, vol 2, pp. 443-461, which he also edits.
* An English translation of the Ethiopic version was published in 1896 by E A W Budge, in The Life & Exploits of Alexander the Great
* An 1896 English translation of the Greek version, by W. A. Craigie, "The Narrative of Zosimus," is in the Ante Nicene Fathers
vol. 10 (in print, vol. 9 if you go online for it, 1896).
This account is legendary (its origins are Medieval), and bears little relation to the kind of traditions that Eisler and Mead dealt with.
Ahh, here is what I was thinking of:
Arthur Cushman McGiffert's 1890 translation of Eusebius' "Church History," in Nicene & Post Nicene Fathers
(NPNF) series 2 vol 1, footnote 509:
῾Ραχαβείμ, which is simply the reproduction in Greek letters of the Hebrew plural, and is equivalent to “the Rechabites.” But Hegesippus uses it without any article as if it were the name of an individual, just as he uses the name ῾Ρηχαβ which immediately precedes. The Rechabites were a tribe who took their origin from Jehonadab, the son of Rechab, who appears from 1 Chron. ii. 55 to have belonged to a branch of the Kenites, the Arabian tribe which came into Palestine with the Israelites. Jehonadab enjoined upon his descendants a nomadic and ascetic mode of life, which they observed with great strictness for centuries, and received a blessing from God on account of their steadfastness (Jer. xxxv. 19). That a Rechabite, who did not belong to the tribe of Judah, nor even to the genuine people of Israel, should have been a priest seems at first sight inexplicable. Different solutions have been offered. Some think that Hegesippus was mistaken, — the source from which he took his account having confounded this ascetic Rechabite with a priest,—but this is hardly probable. Plumptre, in Smith’s Bib. Dict. art. Rechabites (which see for a full account of the tribe), thinks that the blessing pronounced upon them by God (Jer. xxxv. 19) included their solemn adoption among the people of Israel, and their incorporation into the tribe of Levi, and therefore into the number of the priests. Others (e.g. Tillemont, H. E. I. p. 633) have supposed that many Jews, including also priests, embraced the practices and the institutions of the Rechabites and were therefore identified with them. The language here, however, seems to imply a native Rechabite, and it is probable that Hegesippus at least believed this person to be such, whether his belief was correct or not.