The attached is the best shot I could get. There is another vertical bolt that goes through the channel that is not visible, there are two bolts that go through the cross sill end bracket and the bed side angle bracket, these two bolts are closer together than the other angle bracket to cross sill bolts.
The rear horizontal bolt goes inside the stake pocket whereas the front horizontal bolt head is exposed on the outside of the bed.
I was wrong earlier about this being the second cross sill back from the front, it is the third (if you count the front one). This cross sill also has bed mounting bolts that go into the frame. There is one floating cross sill between the front cross sill that the bed front bolts to and this one.
