Ebay item 120956660274. Starting at $400, an M. Brown 564. No bottom pics but seller says it's from 1960. I knew this color was continued in keysets beyond '57 from Paul F's site, but 1960 would mean hard plastic M. Brown?
Sold for $807.85. I think this is the first 564 I've seen with the red round button. All the others with red I've seen are newer with the square buttons.
This is also the only brown key set I've seen with the Amphenol plug. All others have been spade ended. The most common brown set I've seen is the 544 4-button set with spade ended line cord. I've seen more of these than single line sets.