Park head cylinder is not used (at least not for IDE hds). You can ignore this setting.
Also, you can edit the setting without erasing any data. Hitting 'Install Drive' will warn you about destroying all data on the drive. However, when you click 'Ok', you will be presented by a requester to choose if you want to edit the settings instead of starting from scratch. If you choose 'Edit' here, and you only change settings that don't change the geometry settings, you should be safe.
Yes, should be. It works for me, ymmv.
PS. This is with OS 3.5 HDToolBox.
