
Mr. Williams's response triggered another thought.
While many of us have not heard of a CM Handbook, it occurs to me that what your folks might want is a handbook that addresses your particular CM situation. Mil-hdbk-61A and EIA-649 Handbook address myriad topics with practical ideas for performing CM principles. However, the handbook your folks are wanting might be a set of procedures that cover the steps in your CM processes.
For example, you might have a procedure (with criteria and thresholds) for CI Selection, another for identifier conventions, one that explains the change proposal process (with subprocedures and instructions for each step in the process), one or more for various status reports, and one or more for verification/audits. I was once a member of a team that had several more or less administrative procedures for conducting the CCB - agenda template and preparation, minutes template and preparation, rules of order, voting, how to handle dissenting opinions, etc.
If that's the sort of thing they are talking about, it's actually well worth it in the long run because everyone knows where they stand.