We have a Unity server with failover configured. Off box exchange and ad.

Voice mail only environment. These boxes are currently running server 2000. We plan on getting a Dirt backup off the secondary server and then reloading the servers to server 2003. Then reinstalling Unity 4.0(5) and doing a Dirt restore. Then do a upgrade to Unity 5.0(1). My question is once we have loaded 2003 and Unity 4.0(5). Do we do Dirt restore on both boxes and setup failover between them before we continue with the Unity

5.0(1) upgrade.