The Five Colleges has chosen to follow the community mappings and minimize customization regarding MARC bib to FOLIO instance transformation and MARC holdings to FOLIO holdings. The FOLIO Services by Ebsco (FSE) json rules are pulled from the default community rules.
MARC to Instance json mapping: https://github.com/FOLIO-FSE/migration_five_colleges/blob/master/mapping_files/marc_to_instance.json
MFHD json rules: https://github.com/FOLIO-FSE/migration_five_colleges/blob/master/mapping_files/mfhd_rules.json
Item record field mapping is not defined by the community. The 5C mapping in use is here: https://github.com/FOLIO-FSE/migration_five_colleges/blob/master/mapping_files/item_mapping.json