I've never seen a Xeon without a heat sink, I don't believe they are designed to run without one.

Indeed, even the oldest, slowest Xeons shipped in SECC cartridges with integrated heatsinks.

But that was several years after the book cited by the GP was published (1994, shortly after the release of the original Pentium).

The first Xeon looks to be released 1998, so sounds about right