30 standard roadster package tray

[wbs]

hello thank you in advance
how does the top wood piece of the seat back which is flat with an upward curvature attach or fit into the sheet metal package tray?
i hope i am using the correct word for the package tray.
the tray on the leading edge is flat, so it seems the wood could not screw to it. the rear of tray has compound curves top and front to back. if the wood were to fit in tray rear, it seems it also would have to have compound curve.