Over the years (esp. the early years of their popularity), the Don Camillo books were re-released in various omnibus editions (two or more of the titles under one cover). The only one I own, and can therefore tell you a little bit about, is a special one that came out in 1980, comprising the first five of the six books (i.e., all but Don Camillo Meets the Flower Children). It was issued by the British publisher, Gollancz, as a kind of companion to a then-upcoming Don Camillo TV series by the BBC--in fact, the book's dust jacket features photos of the two lead actors (Mario Adorf and Brian Blessed) in the roles of Don Camillo and Peppone (respectively).

THE WORLD OF DON CAMILLO. LONDON: Victor Gollancz, Ltd; 1980.

Includes (with exceptions noted below) the texts of The Little World of Don Camillo, Don Camillo and the Prodigal Son (aka, in US, Don Camillo and His Flock), Don Camillo's Dilemma, Don Camillo and the Devil (aka, in US, Don Camillo Takes the Devil by the Tail), and Comrade Don Camillo.

Exceptions, and other things you won't find in this volume:

• the introduction to The Little World of Don Camillo ("How I Got Like This")
• the introduction to Don Camillo and the Prodigal Son ("The Little World"),
• the story "Appointment at Midnight", which is final chapter of the American volume Don Camillo and His Flock, but which was never included in the British counterpart, Don Camillo and the Prodigal Son.
• part of the "Introduction" to Don Camillo's Dilemma (basically, that Intro. is shortened and moved to the beginning of the entire volume)
• the stories "The Chest of Drawers" and "The Snowstorm" (two stories from the American volume Don Camillo Takes the Devil by the Tail which were never included in the British counterpart, Don Camillo and the Devil)
• the afterward to Comrade Don Camillo ("A Note from the Author")
• the little drawings that accompany each chapter in the original books
• as already noted, book #6, Don Camillo Meets Hell's Angels (aka in US, Don Camillo Meets the Flower Children)

My copy, though it has British publication information, is marked "Printed in the United States of America," and I ordered it in 1984 from a US catalog featuring some Gollancz titles. ISBN 0 575 02933.