I'm trying my best to understand the linked document, but it's  slow going.  In
the meantime, if anyone wants to give me more handholding, I'm guessing so far
from my reading of the linked help doc that more information will be helpful.

As far as I can tell, the site from which I want to mirror the pages and
embedded images uses two query strings, like this:

<http://www.site.com/bla/catalog.php?showitem=12345>