Does anyone have any experience or suggestions migrating from Jazz to Atlassian products?

I am part of a pilot team that must migrate work items to JIRA, and source control (with history) to Mercurial/Bitbucket.

I found out there is an API to retrieve work items, but it seems like comments and attachments cant be pulled via the API.

At this stage we dont have access to the Jazz database or the Jazz admin because we are part of a larger organization whereby Jazz is used for multiple teams, so we cant do anything to affect the operation of, or uptime of the other projects.

Is there an intermediary step involved (eg: jazz -> subersion -> mercurial, & jazz -> bugzilla -> jira) we might be able to try? I know there is the JIRAConnect tool available, but seeing we dont have admin rights to the Jazz server this isnt an option.

We arent so worries about builds or plans, we just need to migrate work items and source control.

My thoughts were to convert streams to branches. Is this the right approach also?

Any suggestions on this task?