By rotary are you thinking White rotary? The 117 model# indicates it's a White made machine. The White machines generally used a buttonholer that was attached directly to the presser bar. The top-clamp adapter was removed and the buttonholer went on in it's place. By your description I think that is what you were seeing.
I don't know if a darning foot was ever available but if it's like the White I had briefly I would expect it to FMQ. The thread path is similar to a Singer 15.
Rodney