Holey carp, you've even replaced the ragdoll system! Needless to say, we're anxiously awaiting a release.
As far as replacement music goes, I suppose you could search around for Creative Commons-licensed music. My friend found a really good music track licensed under CC that we were able to legally use in a game we made for a competition. I couldn't recommend anything specifically because I don't know how the game feels to play, or what kind of music you had in mind.