I suggest doing migrate import/export from production to R77.30 VM.
In that VM remove all the database revisions and run pre-upgrade verifier.
Deal with the findings in R77.30, things like legacy services, non-unicode characters in the object names, etc..
Then, when the verifier shoes no red flags, perform migrate export using R80.30 migration tools.
Get the export file downloaded.
Shutdown R77.30 VM and setup R80.30 VM with latest JHFA.
Perform migrate import.
Save config and migrate export again.
Resultant file should be imported in production on freshly installed R80.30 management, either hardware or VM with no issues, so long as you maintain the same name and IP.
For the gateways, save Gaia config, snapshot, backup.
Download the resultant files.
Perform the "Connectivity" upgrade on cluster members.