Strangely, this has a clear antecedent in The Book of Skulls (1972) by Robert Silverberg, which definitely seems like the kind of thing Swanwick would have read. (The Book of Skulls is, especially compared with a lot of other science fiction, very much set in the world of early 1970s college students, and Swanwick is exactly the same age as the four main characters in the story.) Moreover, in Silverberg's story, the division of a group into four roles is fairly easy to remember, since (unlike in Vacuum Flowers) it plays a central part in the book's plot.
Here is the description of the hunting party, with the four the roles that Ned envisions for himself and the other three protagonists, as the components of their "receptacle":
A book I was reading not long ago drew a structural metaphor of society from an ethnographical film about some African bushmen out hunting a giraffe. They had wounded one of the big beasts with their poisoned arrows, but now they had to follow their prey across the bleak Kalahari, chasing him until he dropped. There were four of them, bound in tight alliance. The Headman, the leader of the hunting unit. The Shama, the craftsman and magician, who invoked supernatural aid when needed and otherwise served as the conduit between the divine charisma and the realities of the desert. The Hunter of Beautiful One, famous for his grace, speed, and physical strength, who bore the hardest burdens of the hunt. Lastly, the Clown, small and freaky, who mocked the mysteries of the Shaman, the beauty and strength of the Hunter, the self-importance of the Headman. These four constituted a single organism, each essential to the whole of the chase.
As noted by Adamant in a comment, this might be a case of one author (Silverberg) inventing something and a later author (Swanwick) mistaking it for a real historical phenomenon. In any case, I think there is a pretty good chance that this is where Swanwick got the idea. However, if the characters in this four-member hunting party were not actually originated by Silverberg for The Book of Skulls, Ned's description quoted above may provide some useful clues as to where the concept had previously appeared.