First restoration-need wood bed help

[Texasupton1]

I would like to start by saying what a great site this is. It has been very helpful in starting my first restoration, a 83 GMC SWB. I will post details on that later, but for now I have a question on my wood bed. I started to remove the bolts, metal strips, and rotten wood last night. FUN. As I got into it, it looks like once all of this is removed the remaining bed and walls will basiclly be just setting on the frame. It looks like the wood is "sandwiched" between the sides of the bed, and where it attaches to the crossmembers, or is this just an illusion and the wood is actually just tucked under the outter edge and and bolted in place? Is this right or will I discover the bed is actually attached in another way and is not loose once all of the wood is removed? I was thinking the wooded part is just a floor, and removing it and replaceing it did not effect the structure of the sides or require the entire bed to be either lifted or removed to put the wood under it?? My plan is to go back with treated 3/4" plywood for now since I will use the truck daily, using only one metal strip down the center to hold in in place, and tucking the outer edges under the metal angle along the sides. Thanks for any photos and help.