Pages 317-355 of the Dell edition; original Pocket Books edition pages 263-294; about 90 to 100 percent of an ebook. In other words, Part Five.
This is a chapter that seems to heavily parody Joyce, although I will let the Joyce scholars explicate in the comments.
Note that the final initiation in this section takes place under the influence of a hallucinogen, and that as I mentioned earlier, it has been suggested that the Eleusinian Mysteries were carried out with the help of a mind-altering drug. The connection between the ancient Greek rite and what happens to Joyce, Einstein and Babcock is made explicit in the text: "One night in the caves of Eleusis is enough for a lifetime, as the Greeks knew." (Page 352.) Note also that the initiation into finding new ways to see is the heart of Wilson's literary efforts. See, for example, the first sentence of his last book, Email to the Universe: "This book intends to change your way of perceiving/conceiving the world, without drums or drugs or Voodoo, simply by using words in certain special ways."
General Cambronne (page 330, and elsewhere) refers to an alleged incident at the Battle of Waterloo.
"I never knew just breathing could be so marvelous" Page 337. Possible double meaning, e.g. being alive is marvelous. But also meditation involving breathing is important in the East; there is yogic breathing, the awareness of breath meditation that is the most important practice in Vipassana, etc.
"hell to be the child of a genius," page 343, I have wondered if minding the children was mainly Arlen's job.
"He is like a refiner's fire," Malachi 3:2. Quoted in Handel's "Messiah." Handel was a favorite composer of Beethoven, as RAW no doubt knew.
"Beethoven probably explains it better than physics," and a reference to the "quantum symphony," Page 334. Beethoven, again, appears as a artist who represents the ecstatic experience. Note also that the list of the Secret Chiefs, pages 322-324, include three composers, two real, one satirical: Beethoven, Mozart and PDQ Bach.