Thanks for the responses.
The update went pretty smooth though ran into one minor glitch which I suspect is because I didn't upgrade the primary device first as a reboot of the secondary resolved it. I was getting messages like "master_decrypt failed during rekey" which wasn't allowing the confsync between the devices to work. Once a final reboot of the secondary device was done this resolved itself.
Other things that I noticed was it took about 11 minutes for each of the LTMs to reboot which isn't to bad except for the fact that at 3 in the morning it seems like an eternity before the pings start coming back. I also had new features after the re-activation of the license keys which wasn't expected but didn't cause any problems. Overall the upgrade took just over an hour to complete.
When it was all said and done I followed this procedure for the upgrade:
1. Run iHealth against configs on both devices
2. Re-activate the license keys on both devices
3. Install new image and HF on secondary device, reboot on new partition
4. Fail-over to secondary and perform verification of services
5. Perform step 3 on primary device, currently temporarily in standby
6. Fail back over so primary is active and verify services
7. Restart the standby device to get confsync working
In the future I will deal with some extra fail-overs and perform the update on the primary/active device first.
Thanks again!