bed mount question

[rageagainstphil79]

I have a question about the position of the bed mounts on my '66 short bed. The PO has welded the bed to the frame and I got to looking around more as to why he did that and the bed mounts at the very back of the bed are wider than the frame. It is still a trailing arm frame and measurements on my frame are the same as my '64 long bed so I don't think the frame has been swapped out. Just wondered why the mounts on my short bed are wider than the frame. Thank you in advance for any help.