Dave, the bed angle strips on the inside of the box side do sit on top of the wood. There are bolts that anchor down through the strip, then wood, then the crises sill and then frame. The wood sits on the cross sills and the strips and the side angle strip sit on top. It may be hard to see from Tim's photo if you're unfamiliar with how these old trucks go together.
When you install your bed wood you start on the outside, slide the boards in and under the strip and then work inwards.
The only trucks I've seen that have a lip under and the angle strip on top of the wood are on the front bed panel of 1 tons.
