Remeber when you are going backwards you may enounter issues in the older versions esp. if there is something done in 8 or 8.5 that does not exist in 7 (new tools/features). Deleteing the history may be the way to stop that, but there is no guarantee, you may still encounter issues along the way.

Autodesk and Alias do not support doing this as it is not recommended. The only other way can see it working is to export the file as an fbx file and import it into 7. This would be the recommendation I would give to anyone swapping from app to app.