john,
In rereading these posts, I keep seeing new things that I either hadn't recognized or didn't pay attention to the first few times around. So help me out, if you can:
Your very first photo on page 1 of this thread you posted this picture. I highlighted the parts in the box:

You asked if anyone could identify these parts in the box. Do you think these are the inside of the frame rails, either at the front, mid or rear sections of the frame. If so, was your point that the strengthening to the frame was done at a later date (after these photos were taken), since these inner sides of the frame were disassembled at the time of these pics?
I couldn't see any replies focusing on these parts, so I thought I'd try to clean up a few loose ends (no pun intended).
For reference, here's #57's rear frame:
