The migration process from a sitebuilder site to a siteworks site is a three-phase process. The first two phases are automated, and the third phase requires manual intervention by the webmaster.
The migration starts with an automated export of the sitebuilder site. This export generates XML descriptions of the objects within the site, and images and pages.
A second phase then uses the generated data to populate a siteworks site. This is automated and consists of loading the migration plugin into wordpress and following a few instructions to migrate each type of object.
The result of the above is a converted siteworks site, which can then be edited by the web administrator to perform the final manual tweaks.
The code corresponding to the conversion of the sitebuilder export file into the siteworks import file is in the repository u3a-siteworks-migration.