Upgrade Active/Passive Cluster with new Hardware

Hi everybody,

i want to update my two ASG 425 to UTM9. Additional to this I want to change my old ASGs with two new ones from the hardware refresh program. The new ASGs have been shipped with UTM9 installed, my old active/passive cluster is currently at 8.309.

Would this be a possible upgrade szenario for me:
1) Downgrade both new ASGs to 8.309
2) Shutdown one of the old ASGs
3) Add one new ASG to the cluster and wait until the sync has finished
4) Perform a failover to the new ASG
5) Shutdown the second old ASG
6) Add the second new ASG to the cluster and wait until the sync has finished
7) Perform a failover to the second new ASG
8) Start the migration to UTM 9.00X

Thanks,

Sam