As you know, Firebird 3.0 RC1 source code was already tagged in Firebird Project repository, but its official installer will be released a bit later. For those who don't want to wait, we have created the unofficial installer of Firebird 3 RC1 - it contains 100% source code of 3.0 Release Candidate 1, just available earlier than the official installer. So you can download Firebird 3.0 RC1 Unofficial Installer and get Firebird 3.0 RC1 now.
Please remember that Firebird 3.0 RC1 is not a production version, but it is very good to test your databases and applications.
If you see any problems with the migration, our company (IBSurgeon) offers complete Firebird Migration service: we help enterprises to go through migration of very complex databases quickly and smoothly.