Over the weekend I was looking for music to Come, Ye Thankful People, Come, and ran across Open Hymnal which has a nice collection of hymns in ABC. Unfortunately, it didn't have the one I was looking for, so I continued searching and found Cyber Hymnal, which did have the hymn.
Unfortunately, the Cyber Hymnal / Net Hymnal folks store their hymns as NoteWorthy Composer files (see their FAQ), and the NWC binary file format has no public specification. Luckily, a number of brave souls laid the groundwork (source here and here) for a binary-NWC-to-LilyPond converter. The original wasn't working for me, so I've put in some time rewriting it and cleaning things up. I've also merged in Hans de Rijck's 1.0 version.