I think I figured out the best way to do this. Make the default file size humongous, like juggungous, ludacris big to get all the mp3'* into one file (since I kept this drive to zero fragmentation and disk tuned, this should pose little problem). Then save the first cluster to be labeled as an mp3. So far, the random 200 MB chunks I've tried have been in alphabetical order, song-wise, so I can use my old song list to name the pieces as I go.
About ~7 GB should do it.