"I don't know if this helps...."

Eleonore Jewett, The Hidden Treasure of Glaston, 1946.

Young acolytes at Glastonbury Abbey in the 13th C meet historical
part-players and discover Arthur's treasure. Loosely based on a legend that
Arthur's tomb and his and Guinevere's until-then preserved bodies came to
light there in the middle ages.

I read it in 1962 or so, and must have acquired my copy at a yardsale over
the last two decades.

David Formanek
Cyrus E. Dallin Art Museum
Arlington MA 02476