better ensure it is indeed your music, because Dropbox will likely report infringements of copyright

Don't they only do that when placed in shared folders?

Some of my Dead could maybe cause a problem (though it was all once freely available on archive.org).

Imagine the uproar if Dropbox started removing files from people's personal, private folders due to alleged copyright infringement.

They could theoretically do this in a way that doesn't really invade privacy (by using only hashes), but the controversy would probably kill Dropbox.

So long as it is no being publicly shared, Dropbox shouldn't have an issue.