Unknown Brackets under bed

[stope4]

I have a 71 fleetside short bed. There appears to have been some brackets under the bed on the frame rails and frame rail cross brackets that I have no clue what they were for. Here are some pictures showing the cut brackets. In the first picture there's a cut bracket in the middle of the cross member and one on the frame rail. Can anyone identify what these were for.



This is the third cross member from rear of truck. Theres another cut bracket on the other frame rail across from the one in the picture.Here's a better view of the bracket welded to the frame rail.



The following is a picture of a bracket that was cut and is bolted to the frame rail in same place as the bumper brackets. There is another one on the other frame rail. Could this mean my truck started out with a different bumper.




Any help would be appreciated.