OK, I didn't do it all by hand. I laid out row/column numbers in Excel and pasted them into text blocks in Gimp column by column. Here's the result.
I've also placed the initial groups on the map (not shown here so don't strain your eyes), and I'm almost ready to start doing actual terrain / feature updates, which was the entire point of this exercise. I was thinking about using the new TiddlyWiki5 for this, but I'm not sure I want to dive into that yet. By my brief look, it seems to have gotten very script-oriented, and I'd rather just write stuff. On the other hand, it's much prettier.