I would bet that a very well finished piece of 4x8 oak plywood would be hard to distinguish from planks if done right. It would be relatively simple to use a router to even recess the bedstrips if you wanted to. The only issue would be the width in some vintages but I am sure a little creativity with some metal strips along the edge would hide that.
And if it is being used for "work" then I'd see nothing wrong with an exterior grade plywood being used.
Seems lots of people forget these trucks didn't come with all these exotic wood beds you see now.
