This 1987 soft-cover publication is long out of print, but copies in excellent condition remain widely available from sources such as eBay and Amazon. The book is a very useful reference, its most valuable feature being the wealth of photographs of often-obscure engines for which images are otherwise difficult to locate. It is organized in a strictly alphabetical sequence, with neither the country of origin nor the displacement of a given engine affecting its place in the sequence in any way. As a result, it's very easy to check to see if a given engine or brand is included.
The one word of caution is that the limited factual information included with the engine pictures is often in error or at least misleading - it does not appear that a great deal of focused research went into the book's preparation. Accordingly, the book should not be relied upon as an authoritative source of factual information. That said, it remains an extremely useful reference, and one which belongs in every serious engine collector's library.