On a 47-51 1st short step you should have cross sills at the following locations:
One at the 1st hole in the bed strips
One at the 3rd hole in the bed strips
One at the 5th hole in the bed strips
A rear cross sill at the back.
The angles are offset 7/8" to 1" to the rear of the truck
The 4th hole back (on the angle) does not line up with the bed strips.
Hope this helps.