sys_journal_field is the correct place to import those. Using autoSysFields(false) on gliderecord should get you what you need as far as setting your own values for sys_created_on and sys_created_by. Here is a sample script that inserts a record into sys_journal_field and sets my own created fields:
var gr = new GlideRecord('sys_journal_field');
gr.autoSysFields(false);
gr.newRecord();
gr.sys_created_by = 'test.user';
gr.sys_created_on = new GlideDateTime('2017-04-01 02:30');
gr.element = 'comments';
gr.name = 'task';
gr.element_id = '53f367e20f123200e23909bce1050e27';
gr.value = 'This is a test journal entry';
gr.insert();
In your case, if you are doing this in an import, then an onbefore transform script should be all you need where you would do this: target.autoSysFields(false)
and then map your sys_created_on and sys_created_by from the source file. Just keep in mind that if you do this in a transform map, you need to probably put the sys_ids of the incidents in your excel file because it won't be able to look it up by incident number. Or you can write into your onBefore script to lookup the sys_id by incident number and put that in the target record.
Notice that I put the name field above as "task". this is because that is where comments and work_notes reside. so make sure you set "task" for the name field and not "incident"
Then, for getting it to display in the activity feed, we need to refresh the history, try this in an onAfter transform script. I tested it on my istanbul instance, but should work on Geneva as well:
var ghs = new GlideHistorySet(target);
ghs.refresh();
Let me know how that comes along. I tested the above GlideHistorySet part and it is not showing the proper date and user there, though the journal field table does have it correct. I will see if I can figure out how to get that history updated properly.
