This is really cool to see actual photos of this stuff. The '58s were certainly a rare design as far as the rear suspension is concerned.
Where your upper control "arm" or "rod" attaches to the frame... on my car there was a "torn spot" there on the right side. (I welded a stainless patch over that old injury this past winter. I have leaf springs on my '58 and dont need that mounting hole anymore.)
Based on my findings while lying on my back under the car for most every weekend this winter, I'd say that my car suffered a fender-bender on the passenger side at some point in the past.
She tells no tales of her past though, no matter how nice I speak to her....
Sorry to high-jack your thread with my non-contributory comments!