I seem to recall I successfully moved a forum into a completely different forum. It just required moving one forum into another, in exactly the same way that you'd move a sub-forum around within a single forum. It might have required that the admin user name or email address is required to be the same in the new parent forum. I forget! Of course, it required that users of the "old" forum had to register at the new parent.
Of course, doing something similar with a mail list archive will break any subscriptions to the mail lists, so how feasible it is will depend on what access and posting rights you want under the new regime. Are two of the lists now obsolete? Do you only require future posting rights in one of them? Tell us more about your requirements.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.