Service Now Helper Script to Syncronize the Journal fields between Instances. If you can, it is recommended to just sync the text using getJournalEntry. This script will replicate all Activity log history, Audit records, and Journal table entries so it looks like it originated from the target instance.

JournalSyncHelper - Include.js

/*Name:         JournalSyncHelper
 * Description:  Helper class for Masco Milgard 2 way sync. Allows Journal fields (Comments, Worknotes) to be synced.
 *               Helper functions to package up Comments and WorkNotes to a JSON String. Also function to decode and insert
 *               packaged journal field back in SN.
 * Author:       Paul.Senatillaka@fruitionpartners.com
 *
 * Version: 2.0 - 10/11/13 - Rewrite from v1 to better handle large comments and numerous other fixes.
 */
gs.include("PrototypeServer");
var JournalSyncHelper = Class.create();
 
JournalSyncHelper.prototype = {
    initialize: function () {},
 
    /*
     * Package up Journal entries (Comments, Worknotes) into a JSON Object for tramissions over WS.
     * Function used by sending system.
     */
    packageJournal: function (recordId, includeWorkNotes) {
        try {
            var grJournal = new GlideRecord('sys_journal_field');
 
            if (includeWorkNotes) {
                //Query for Unsynced Worknotes or Comments for a given Record
                grJournal.addEncodedQuery("element_id=" + recordId + "^u_synced=false^element=work_notes^ORelement=comments");
            } else {
                //Query for just Unsynced Comments for a given Record
                grJournal.addEncodedQuery("element_id=" + recordId + "^u_synced=false^element=comments");
            }
            grJournal.orderByDesc('sys_created_on');
            grJournal.query();
 
            var packedJournal = [];
            var json = new JSON();
 
            while (grJournal.next()) {
 
                //Lookup Journal User
                var grUser = GlideRecord('sys_user');
                grUser.get('user_name', grJournal.sys_created_by);                
 
                //Truncate extremely large journal entries
                var journalValue = grJournal.value.toString();
                if (journalValue.length > 20000) {
                    journalValue = journalValue.substr(0,19960) + "\r\n\r\n[Message Truncated to 20K Characters]";
                }
                //Create object for JSON Array
                var entry = {
                    element: grJournal.element.toString(),
                    value: JSUtil.escapeText(journalValue),
                    sys_created_by: grJournal.sys_created_by.toString(),
                    sys_created_on: grJournal.sys_created_on.toString(),
                    name: grUser.name.toString()
                };
 
                packedJournal.push(entry);
 
                //Marked Journal entry as Synced so we don't grab it next time!
                grJournal.u_synced = "true";
                grJournal.update();
            }
 
            return json.encode(packedJournal);
        }
        catch (err) {
            gs.logError('Failed Packaging Journal fields for Incident: ' + recordId + " \n Error Msg: " + err.toString(), "Record Sync");
        }
    },
 
    /*
     *  Unpackage JSON Journal object and insert into Journal Table. Also insert into Audit, and History Line table
     *  so entries show up correctly in the Activity Feed.
     *  Function used by reciving system.
     */
    syncJournal: function (recordId, jsonJournal) {
        try {
            //Write to System Log
            gs.log('Starting sync of Journal Fields for Incident: ' + recordId, "Record Sync");
 
            var json = new JSON();
            var journal = json.decode(jsonJournal);
 
            //Lookup History Set. We need this to insert Audit and History Line (Activity) Records
            var grHistorySet = new GlideRecord('sys_history_set');
            if ( !grHistorySet.get('id', recordId) ) {
                gs.log('Debug: History Set not found for Incident: ' + recordId, "Record Sync");
            }
 
 
            //Query Journal Field
            var grJournal = new GlideRecord('sys_journal_field');
            grJournal.addEncodedQuery("element_id=" + recordId + "^element=work_notes^ORelement=comments");
            grJournal.orderByDesc('sys_created_on');
            grJournal.query();
 
 
            //Loop through source Journal entries
            for (var i = 0; i < journal.length; i++) {
 
                //Check if Journal entry Exists                
                if ( !(grJournal.find('value', journal[i].value) && grJournal.sys_create_on == journal[i].sys_created_on) ) {
 
                    //Write to Import Set Log
                    log.info('Creating ' + journal[i].element + ' for: ' + journal[i].value);
 
                    //Insert Journal
                    var grNewJournal = new GlideRecord('sys_journal_field');
                    grNewJournal.initialize();
                    grNewJournal.name = 'task';
                    grNewJournal.element_id = recordId;
                    grNewJournal.element = journal[i].element;
                    grNewJournal.value = journal[i].value;
                    grNewJournal.sys_created_on = journal[i].sys_created_on;
                    grNewJournal.sys_created_by = journal[i].sys_created_by;
                    grNewJournal.u_synced = true; //So we don't sync back later
                    grNewJournal.autoSysFields(false);  //So Created On and By don't auto populate
                    grNewJournal.insert();
 
                    //Insert Audit
                    var grAudit = new GlideRecord('sys_audit');
                    grAudit.initialize();
                    grAudit.documentkey = recordId;
                    grAudit.internal_checkpoint = grHistorySet.internal_checkpoint;
                    grAudit.tablename = 'incident';
                    grAudit.fieldname = journal[i].element;
                    grAudit.newvalue = journal[i].value;
                    grAudit.oldvalue = "JOURNAL FIELD ADDITION";
                    grAudit.user = journal[i].sys_created_by;
                    grAudit.sys_created_by = journal[i].sys_created_by;
                    grAudit.sys_created_on = journal[i].sys_created_on;
                    grNewJournal.autoSysFields(false);  //So Created On and By don't auto populate
                    grAudit.insert();
 
                    //Insert History Line
                    var grNewActvity = new GlideRecord('sys_history_line');
                    grNewActvity.initialize();
                    grNewActvity.set = grHistorySet.sys_id;
                    grNewActvity.audit_sysid = grAudit.sys_id;
                    grNewActvity.field = journal[i].element;
                    grNewActvity['new'] = journal[i].value;
                    if (journal[i].element == 'comments') {
                        grNewActvity.label = 'Synced Additional Comments';
                    } else if (journal[i].element == 'work_notes') {
                        grNewActvity.label = 'Synced Work Notes';
                    }
                    grNewActvity.user_id = journal[i].sys_created_by;
                    grNewActvity.user = journal[i].sys_created_by;
                    grNewActvity.user_name = journal[i].name;
                    grNewActvity.update_time = journal[i].sys_created_on;
                    grNewActvity.internal_checkpoint = grHistorySet.internal_checkpoint;
                    grNewJournal.autoSysFields(false);  //So Created On and By don't auto populate
                    grNewActvity.insert();
 
                    //Write to System Log
                    gs.log('Successfully synced journal entry: ' + grNewJournal.sys_id + ' by:' + grNewJournal.sys_created_by + ' for Incident: ' + recordId, "Record Sync");
                }
 
            }
 
            //Update History
            if (typeof GlideHistorySet != 'undefined')
                GlideHistorySet(grHistorySet).refresh();
            else
                Packages.com.glide.audit.HistorySet(grHistorySet).refresh();
 
            return true;
        }
        catch(err) {
            gs.logError('Failed Parsing and Inserting Journal fields for Incident: ' + recordId + " \n Error Msg: " + err.toString(), "Record Sync");
            return false;
        }
    }
};

New to this - lines 131 and 151 reference grNewJournal, shouldn't they reference grAudit / grNewActivity?

Yes they should, though unfortunately this hasn't solved my issue in Geneva with the activity feed showing the incorrect date.