Currently I am trying to seperate the under frame from the bottom plate which is attached to the chassis assembly of a 2-8-0 Consolidation steam locomtive. It is loose but will not totally separate. I have removed the two screws which attach to the chassis assembly.
On the 2-8-0, the drive wheel brakes are molded directly to the bottom plate. So... you will have to manipulate the plate a little to move the brakes around the wheels. I have done this many, many times. The first time was a mystery to me, too. It can be done. Just be a little patient.
Regards,
Jonathan