Enak,
You are lucky the Bureau even has it on the database
Seriously, there was a report on the tornado from the Bureau but until the 1990's. Neverthless, the Bureau has not really rated tornadoes until the 1989 Elsmore, NSW tornado to my knowledge. Was the Brisbane tornado rated? Unless someone has seen the damage and done an appropriate survey, can you really rate a tornado?
Regards,
Jimmy Deguara