Toward Ecosophy

RJ Stewart has an essay titled "The Tomb of a King," which is iirc included as an appendix in The UnderWorld Initiation, which gives some details of the older tradition; Carmen Blacker's The Catalpa Bow has a chapter on the sokushinbutsu of early modern Japan, who followed the same tradition. I also used Burl extensively as a resource, and of course the extensive scholarly literature on Egyptian funerary traditions and on vampirism covers much of the later material. That said, yes, there's a lot of personal inference involved.