I wish you luck finding wood replacement parts for your Chevy PU, at best I think you might find paterns, maybe in Hemmings. Friend of mine has a way of doing it but he's in Italy right now, I can ask him when he returns this week.
Have you thought for framing it out in 1/2" sq tubing? Guy down in Delaware did his chevy up this way, got rid of 90% of the wood in his sedan. <img src="graemlins/pimp.gif" border="0" alt="[pimp]" />