I just finished reading Ishmael Reed's Mumbo Jumbo, in the course of which I made an interesting discovery: Illuminatus! misquotes the book (or, depending on how you look it, Illuminatus! paraphrases it.)
At the beginning of Illuminatus!, on the title page for Book One:
The history of the world is the history of the warfare between secret societies.
-- Ishmael Reed, Mumbo-Jumbo
This is what Reed actually wrote: "Someone once said that beneath or behind all political and cultural warfare lies a struggle between secret societies." I'm not clear if Wilson and Shea were relying upon memory or if they felt the need to rewrite what Reed actually wrote. The Reed quote would arguably have been stronger if Wilson and Shea had actually quoted what he wrote, lopping off the first four words. Note also that the title of the book is wrong. It's Mumbo Jumbo, not Mumbo-Jumbo.
The resemblances between Mumbo Jumbo and Illuminatus! are interesting; both describe the struggles between secret societies, although in Reed's work it's the white monotheists (the bad guys) versus the black polytheists (the heroes). In an interview in The Illuminati Papers, Wilson says, "I didn't read Mumbo Jumbo until about 3 years after Illuminatus! was finished. The same is true of Pynchon's Gravity's Rainbow. The astonishing resemblances between those three books are coincidence, or synchronicity, or Higher Intelligence (take your pick). I love everything Ishmael Reed writes, and I once sent him an official Discordian certificate making him a Pope in the Legion of Dynamic Discord." So the paraphrase from Mumbo Jumbo presumably was inserted late in the publishing process.
Here is a good review of Mumbo Jumbo from one of my favorite critics, Ted Gioia. I am not sure I can agree, however, with Gioia's comment that "you are best served if you come to this novel with a deep knowledge
of history." Ignorance of history is helpful in many places in the section near the end of the book where Reed offers his grand conspiracy theory of history, because the narrative has many jarring mistakes. Constantine was not converted to Christianity in "the late 4th century B.C.," A.D. 378 is not the correct date for the destruction of pagan temples by Emperor Theodosius (the Alexandrian Serapeum was destroyed in A.D. 391 or so), an ancient Egyptian could not have come to South America and made contact with the Incas, and so on.