To help with migration data integrity checks, today I spend the day working on this and created a migration tool which I hope is useful.
Basically, I mapped all the new discourse topic ids to the original forum thread id and moved all that information to the mysql DB of this forum. I think the effort was worth it.
You can now visit the corresponding topic in the new forum via the thread drop down menu:
This feature is available only to registered users (for now).
It took me all day do get these mappings done and working; so I hope our great members find this tool useful.
Also note, if the thread has not been migrated yet, or for some reason it not in the mapping, there will be no "community menu item" in the thread tools menu.
Also note, if the thread is not in a public forum (for example a jailed thread in a spam forum or a topic in the moderator forum), this quick tool will (actually may) not work. This tool is only for publicly visible discussions threads.