Let me make sure I understand what you're trying to achieve. You want the contents of the Notes field from the related incident to be shown on the event's mc_long_msg field, or the other way around?
The information from the incident ticket is usually not sent to the original event; instead, it's the EVENT_INCIDENT_INFO event that gets updated.
You might be able to get the contents of the notes fileld mapped (look at the IBRSDplugin.map file on the AR side), and then trigger a rule to pull the info from the EVENT_INCIDENT_INFO and update the EVENT.
Be careful; however, with creating a loop...