In one catalog, select the desired photo(s) and then use File->Export as Catalog
In the 2nd catalog, use File->Import from Another Catalog
I did as you suggested and export/import went smoothly. However. All the photos were flagged with a metadata conflict. So I had to select to either "overwrite from disk" or "make no changes". I was a little confused with the "overwrite from disk" but with some experimentation concluded the "make no changes" option was the one to select.
Thanks for the help!