I have not done this myself, but have seen many metal replacements of wood on these early trucks.Mostly done on the doors and mostly in hot rods. The wood frames are pretty basic when you look at the design, and if you have some carpentry skill, you might be able to do some or all of it yourself. If not, try talking to a local cabinet maker. With plans or templates he might be able cut the peices for you to assemble.
The important part is to obtain high quality, kiln dry wood, usually ash.
