| Quote #1
who bared their brains to Heaven under the El and saw Mohammedan angels staggering on tenement roofs illuminated (line 5)
How does the speaker know the angels are Islamic, or "Mohammedan"? There is no indication from these lines. Ginsberg was less interested in complicated theological differences and debates than in the sheer power of religious imagery. He used images and symbols from many different religious traditions.
| Quote #2
who vanished into nowhere Zen New Jersey leaving a trail of ambiguous picture postcards of Atlantic City Hall (line 20)
The Beats had an affinity for Asian literature and Zen Buddhist writings in particular. Is the speaker suggesting that "nowhere," "Zen," and "New Jersey" could be the same place? "Zen" isn't actually a place, except metaphorically: it's a state of enlightenment characterized by the absence of thought or feeling.
| Quote #3
who studied Plotinus Poe St. John of the Cross telepathy and bop kabbalah because the cosmos instinctively vibrated at their feet in Kansas (line 24)
"Mysticism" refers to religious practices that aim for an immediate connection with the divine. Kabbalah is a form of Jewish mysticism, and St. John of the Cross was a Christian mystical writer. The speaker of Howl does not show a wide knowledge of religious traditions, but rather an interest in specific (and generally radical) thinkers from several different faiths.