It's super late, but Halo DLC for 3,4, Reach, and Wars is finally free. Maybe I can finally get some of those old achievements.
Halo 3: https://marketplace.xbox.com/en-US/Product/Halo-3/66acd000-77fe-1000-9115-d8024d5307e6?DownloadType=GameAddon#LiveZone
Halo...