Just FWIW the correct name of the parts is Stake Sides. Maybe I'm too close to the subject as I have never heard them called "fences" in my 43 years in the business. I got a laugh from that so Thanks. Needed a laugh today.
The factory built stakes were built with rivets and generally had oak posts and slats. Some used pine but the clear lumber became so expensive and difficult to get in the 80's that all of them went to steel stakesides only being offered. No one now offers wood sets that I'm aware of. Stakes were generally 1x 6 planks. Post size depended upon the manufacturer but common today is 1.5"x 3.5". I prefer tapered posts/pockets so they stay put.
Great looking truck. I had a 66' just like it in the 70's with 305 V6 and 4 & 2 speed.