Tim wrote:

"Interesting -- the one on the right appears to be "T-section" (I don't know the technical term) and the one on the left a more modern U-section sideframe. I think the one on the right was soon to become prohibited for unrestricted interchange."

Tim,

"T", "L" and "I" section side frames were permissible in interchange until January 1, 1957.

Guy Wilber
Reno, Nevada