I took my Word doc and saved it as a "Web Page (filtered)." By choosing the "filtered" option, the html was much, much, MUCH cleaner. I converted the file with Calibre and it came out perfectly, as far as I can tell. I couldn't stomach going through every single page again, but I hit a lot of them, including the problem pages, and it all looks good!
As Mr. Ploppy says, it's about a 10-minute process!
So, apparently, my hours of torment can be attributed to Word's bloated html created when you save as a Web Page, not filtered.
I'll send the clean html file to Ghostwriter Publications.
Thanks, all, for letting me rant!