Earlier it was questionable if 3.x functions should be loaded at all as there are many 3.x functions that has unsafe implementations (adding methods to Scope, or every Object). As we now have safety checks when loading 3.x functions this is less of a concern.
Adding 3.x loading as Glenn Sarti shows should be easy and then "just work".
Legacy Ruby Functions, also known as Version 3 Functions, will now be available from the cached lib directory. Previously only Version functions were available. Note that functions that exist in both Version 3 and Version 4, will still use the Version 4 implementation.