Any caveats would get washed out when the property was transferred, unless there were excess funds in which case they would then go to pay the lodger of the caveat.
You can find out who the architect originally did the work for and then look them up in google with the word insolvency after it. You should find it. It the guy made $400K their should be enough left over to pay the architect then.
I would have a chat to the administrator/liquidator if there is one. If the architect has submitted a claim then the administrator may be able to deal with those plans and sell them to you.