where did you get what you show in that box above? I have never seens any part of a database backup that looks like that or any part of the database tables etc.
You didn't mention cleaning your 3.0.x database (STK) before starting the upgrade.
Since you mentioned restarting from scratch, I suggest doing that, including truncating the search tables (less data to process).
And since you had a timeout, try it on personal webserver or using CLI.
Spelling is freeware, which means you can use it for free.
On the other hand, it is not open source, which means you cannot change it or publish it in a modified form.
Time flies like an arrow, but fruit flies like a banana.