"To those less convinced, Larner is generous. For me, one
of the grace notes in his study was the wondrous parody
of Marco Polo found tucked in Boccaccio's `Decameron,'
quoted here:"

I have been unable to find any mention of Marco Polo in the Decameron. Can you?

Bill, the operative words here are, I think, "parody of Marco Polo". A parody would not necessarily announce itself as such and hence would not mention Marco Polo.

I haven't read the work you cite. I would imagine that the parody is found in either Day 8 Story 3 or Day 8 Story 9, both of which feature the inimitable duo Bruno and Bufalmacco.