Yeh, I know, more Drupal. But this was a major improvement.
So after I made the custom error pages I then discovered a key weakness in the out-of-the-box Search module: my error pages would come up in search results, because they are just another bit of content, just like this post. The answer was a better search engine, something I had planned on adding eventually, but now I had a reason for sooner rather than later.
Search API to the rescue!
It's time consuming to configure and tweak to get just the way you want it, but you can get it just the way you want it!
Search results now include only what I want them to include, and that includes way more options than I had before, including any media—images and audio tracks—that may be related to a search term. Plus, as I begin re-organizing the topics from the old journal posts (the old site had those but were lost in the translation), those topics are included in search results, and they in themselves are like pre-formatted searches.
I still need to get back to the issue of redirecting traffic that is coming in from old links. That's what I was up to a few days ago, before I went off on a (Drupal) bender.
Update - Rather than adding yet another boring post about the development progress of this site, I'll just update this one to add that I finally got around to dealing with setting up the redirect stuff I was going to do earlier. It was painless.
So I just pushed up the v1.01 tag and I now consider the Carbon Harbor Journal officially back from the dead.