There's a little story behind this one. The 330P4 book was discussed - once- with a publisher who was keen, BUT terms were not discussed and a contract was never signed. Neverthless the would-be publisher decided to ISBN the title, and from there it went into the public domain. It is still a book that I would like to do, but I have two more Ferrari titles out in the next six months, and I am also working on another for about 12 months time. So regretably not much time for P4s at the moment.
Books in the works? Still some hope that these may appear.
"Ferrari 330P4 - The Complete Story" by Nathan Beehl & Paul Skett. ISBN 0954694635. Listed on Amazon UK. AS of 29-Nov 2007, Beehl says that book has not been started yet, but still hopes to do it. Link.