Once A Catholic
Book by Peter Occhiogrosso (Houghton Mifflin Company, Boston, 1987) in which "Prominent Catholics and Ex-Catholics Reveal the Influence of the Church on Their Lives and Work". Includes a chapter with 10 pages about Zappa.
From the backside of the dust jacket:
Frank Zappa: "I can still remember the tune of the 'Kyrie' that they were singing at my confirmation. That lick pops into my head sometimes, and I've wound up playing it on the guitar in the middle of solos – I swear to God."