Mark - Yes. You would essentially create custom fields in either SFDC so the fields sync over into Marketo, or create the custom fields in Marketo itself (these fields will not be pushed into SFDC then). When you import your CSV files, you'll just want to ensure that your CSV file has the relevant data in those custom fields. Alternatively, you can always run a single-flow action to update data in fields for leads/contacts. Hope this helps.