Peter co-authored The Real Frank Zappa Book, which unfortunately is apparantly out of print at the moment. If you can find a copy, it's considered required reading for anyone interested in Frank Zappa. Peter has written books mainly about religion and rock music, titles including "The Joy Of Sects" and "Inside Spinal Tap".
So far the most insightful look at his relationship to
Zappa is provided by means of an interview between him and Vladimir Sovetov,
There's an issue about TRFZB that hasn't been satisfactory explained (as far as I know). In the Marshall interview Frank denies that Occhiogrosso has anything to do with how the book finally turned out. He says that he had to type the book from scratch after having seen PO's version. But Frank has been known to twist and frugg the truth in some cases (notably the destroyed mastertapes), but why should he distract from the truth about this?
From my understanding:
Peter interviewed FZ.
Peter transcribed & edited interviews, provided transitory exposition, and organized into book.
FZ got Peter's draft and tweezed it to his liking.