Brain Tumbler does live on - I still plan to create it as an add-on to work *alongside* Oatmeal, to have a user-friendly way of managing the various custom properties that are required to fully support Psychonauts' data. But we're getting ahead of ourselves with that.
As it turns out the PS2 version of Psychonauts has a lot of leftover files which don't exist anywhere else.
One interesting find is this test level consisting of 4 areas and a central room used to access them.