What book of Eugène Sue's 'The Mysteries of the People' inspired M. Joly's 'Dialogue in Hell Between Machiavelli & Montesquieu', as claimed by U. Eco?

Question summed up: Can anyone help me find the part of Eugène Sue’s The Mysteries of the People wherein a sinister Jesuit plot is unveiled, which may have, through a game of ‘telephone’ by plagiarism, inspired parts of the anti-Semitic forgery, The Protocols of the Elders of Zion?

In one of the essays in his Six Walks in the Fictional Woods, Umberto Eco mentions that the French writer Eugène Sue’s last novel Les Mystères du peuple (in English The Mysteries of the People) includes the revelation of a "Jesuit world conspiracy." Eco claims that this was more or less plagiarized by the French writer Maurice Joly in his Dialogue in Hell Between Machiavelli and Montesquieu, wherein the plot is transferred to Machiavelli (who is a stand-in for Napoleon III). Joly’s book was then, in turn, a major source plagiarized for the infamous anti-Semitic forgery The Protocols of the Elders of Zion. Still following?

Being interested in how conspiracy theories evolve, "borrow," and converge, I wanted to read the original bit in The Mysteries of the People. My issue is that The Mysteries of the People is actually a series of 19 novels and novellas, and Eco doesn’t indicate in his essay in which book this passage appears. Rather than read the whole thing, I was hoping somebody might know, or advise how to narrow it down.

Here’s what I know:

1. An important distinction is that the series in question is The Mysteries of the People, not The Mystery of Paris, another, much more famous, book by Sue. Nor is it The Wandering Jew, another more famous book of his that includes Jesuit villains.
2. The primary English translation of The Mysteries of the People is by Daniel De Leon.
3. 18 of the 19 English translations (as well as some, maybe all, in the original French) are available on Project Gutenberg; the odd one out is available from Google Books.
4. Eco includes a lengthy quote in his essay (see Google Books, pp 134-135 – if the link just takes you to the book, rather than the pages, use the Search Inside This Book function and look for ‘Rodin’). Googling that quote or parts of it only leads you back to the Eco book. So either Eco made it up, or he’s not using the De Leon translation (actually fairly likely, since Eco translated books from French himself).
5. Even doing a text search in the Gutenberg books for some of the most key words in the quote doesn’t turn up an obvious candidate.
6. Eco mentions that this part in the book involves (in a further complicating development) a Monsieur Rodin (a character from Sue’s The Wandering Jew), a Rodolphe of Gerolstein (a character from his The Mystery of Paris), and a Father Roothaan (a real historical figure). I searched all three names in the text, with hits that seemed to be part of what Eco described (‘Rodin’ and ‘Gerolstein’ (but not Rodolphe) occur, but they might be referred to by other titles elsewhere in the text; Roothaan doesn’t appear at all, but he was Superior-General of the Jesuits at the time, and there are references that seem to be to a Jesuit Superior-General – but again, none that seem to include the revelation of a plot).
7. Eco claims he identified "no less than seven pages" of Joly’s book that appear to be lifted from Sue’s. So the source material in Sue isn’t just some passing sentence, it must be several pages worth of narrative.

That the Protocols were stolen liberally from Joly is well-documented. However, any mention of Joly stealing from Sue always points back to the Eco essay. It seems unlikely to me that he would make something like that up with so bold a claim as having found 7 pages worth of cribbing. (Don’t be confused, though, he also talks about this connection his fictional novel Foucault’s Pendulum, which just complicates things more).

I’m not holding out much hope that anyone has actually read The Mysteries of the People and can point me straight to the right book, but I was thinking maybe somebody who knows French lit, or knows how an Italian might translate French into English, might think of something I haven’t and can give me a new clue to pursue.