Thanks to all for your comments. I would be very happy to share plans of the swell pedal assembly if there were any! I made it up as I went along
. You can see more detail if you click through to the Flickr pictures, though. Or I'm happy to send an annotated photo if you PM me.
Re the wood - the basic "desk" construction is oak-veneered MDF, the music stand, cheeks and swell pedals are oak, as is the bench (which was professionally made by Renatus).