it's maybe the biggest Holmesian homage in the series -- just, obviously "How would I do Reichenbach if it happened to Wolfe and Archie?"

Yeah, seriously. I'm always thinking about Moriarty when I think about Zeck, and I wonder if Stout, as he was twining Zeck into the earlier books, already had Moriarty this specifically in mind.

I think the kicker Moriarty-wise is his head--most specifically the word "dome". Holmes's first sight of Moriarty goes:

He is extremely tall and thin, his forehead domes out in a white curve, and his two eyes are deeply sunken in this head. He is clean-shaven, pale, and ascetic-looking, retaining something of the professor in his features. His shoulders are rounded from much study, and his face protrudes forward, and is forever slowly oscillating from side to side in a curiously reptilian fashion. He peered at me with great curiosity in his puckered eyes.

And Archie's goes:

Actually there was nothing to him but his forehead and eyes. It wasn't a forehead, it was a dome, sloping up and up to the line of his faded thin hair. The eyes were the result of an error on the assembly line. They had been intended for a shark and someone got careless. They did not now look the same as shark eyes because Arnold Zeck's brain had been using them to see with for fifty years, and that had had an effect.

One's a serpent, one's a shark, but they both specifically have this great dome of a forehead. It's like "dome" is synecdochic for Moriarty across the board--the song "Macavity" in the musical Cats, about the criminal-mastermind cat, has the line "His brow is deeply lined with thought, his head is highly domed", and it's like BING!