Hmmm it does identify as 0.573 when I start it up, although I'm a little leery of loading my world under these conditions without first backing it up, and since world backups also take a while, I'm worried about doing that while I'm still waiting on the installer to tell me it's done. Said installer is still running since I posted earlier, by the way...
Edit: I guess I could just manually back up the world folder and not be so worried about it. Derp!
Edit edit: It just finished! 26 minutes, I think that's a new record!