You likely will need some hot fixes to get ready for R75.40 (should be your next target; not sure if you can go directly to R77.30). I think you can skip R75.45 and R75.47 for this.
Once you get a working R75.40 management server, do a migrate export for R77.30. At this point STOP.
Install a brand new R77.30 VM on Gaia. Import your exported R77.30 database and verify it works.
When you get to R77.30, then you need the latest jumbo HFA and the new migrate export tools. Run migrate_server to export for R80.40 (for your own safe keeping). Upgrade Gaia with the Blink image if you want and it’ll do the migrate export and import for you.
Verify R80.40 works, then do a migrate_server export for R81.20.
I’d suggest ANOTHER brand new VM install for R81.20, with recent HFA, and import the database export again.
For any troubles you encounter on the way, read the logs carefully. They will tell you what to do to get things fixed. You may need to get an eval license so you can get a fresh IPS database update along the way somewhere. You may also need license upgrades. You may encounter a CP.macro file that needs updating at various points. Usually this is shown in some error output fairly prominently.
Enjoy!