That's. That's pretty much it. I'm just wondering if I can do this and whether it'll work properly. Just shut down the Ubuntu guest, go into the VBox manager, make the folder with the extant blockchain files shared and mount it to Ubuntu's default localnode path, then go back into the virtual Ubuntu machine and start node setup with the blockchain already in place.
P.S.: I would just export/duplicate the files onto the virtual machine instead of linking them but the blockchain is already a good order of magnitude larger than my average size for entire *nix hard drives.