Hi Simon,
The buck you are showing is Chuck Lindquists Coupe and it is built on an original style frame, that is where you start. After you build the first frame for the buck then you can build/weld/fabricate the second one for the actual car.
Since you have the picture of the buck, I assume you reviewed the entire build process at:
http://members.aol.com/chuckcobra/
Contact Chuck and I'm sure he will be happy to share the details. The wood was plywood and I am not sure if it was 1/2 or 3/4.
Tony R.