Lobo:
The angle strips on your bed sides should have been punched for two 3/8 bolts at the bed to frame locations near the back of the bed. All remaining holes in the angle should be 5/16" square. The bed to frame bolts behind the axle in this truck were installed through the angle strip. Just drill out the holes a little over 3/8" for the 3/8 carriage bolts. These angle strip holes should align directly over the matching holes in the rear area of your frame rails.

Hope this helps.

Mar-Ktech