This is a nice seat for a kayak but with the Surfski the seat is incorporated into the cockpit as a one-piece design
in the link below you can see the sketch that Nick was showing a few years back in an earlier post on this topic. I'm looking for an Idea on building this complete unit with wood. as you will see from the image the seat is quite different than a kayak seat.
Walt
http://www.kayakforum.com/cgi-bin/Building/index.cgi/md/read/id/228449/sbj/other-surfski-cockpit-design/

This project is still on hold and still high on my priority list. I did try to mock up a seat last year but found I needed more flexible plywood than I used. I would probably build the whole ski out of 1.5mm ply to keep the weight down, and that would be plenty flexible for the seat.