[summitflier]

I dont see the rails that run along the bottom inside of the bedsides. These have the holes where you line up the cross members. If you're missing the rails, the three in center will just "float" on top of the frame. The smaller one goes in the middle of course.
For the front one set it on top of the flat plates that are attached to the frame in the picture above. I have a wood bed, if you have a metal bed I'm not sure how it works.
But if you still have the wood with the holes drilled, or the metal spacer strips that go between the wood pieces, you can also use those as a template for where the cross pieces go.

I still have some of the wood out of mine, I will take a pic when I get home.