Update to say that I was able to work out a combination approach. Unfortunately my company's existing styles aren't "headers," and I'm not good enough with macros to edit the code to work with our existing styles.

What worked was creating a new list style in a template and pasting each document in, and cleaning up with that old WordBasic command to delete the hard numbering. (Which does in fact work on a Mac!).

About a minute per file, fast enough for me!

Thanks again.