Well Chris, despite the fact that I didn't recognize the first parts you posted, I looked in my HJ parts book and did not see them shown/listed. This afternoon I went out and looked at both of my Js and I think the parts could be a spacer/shim/buffer between the rear spring and rear end. I don't know if this piece is separate or not -
The parts books (both the '51 section and the '52 - '53 supplement) do not show or list it. Does it look like it?