The clip/spring and a piece of felt secures the pulley to the adaptor with some pre-determined amount of "slip" however the adaptor is an interference fit onto the motor shaft. I have recently heard (on another forum) that it is possible to heat the adaptor with a blowtorch and ease the adaptor off of the shaft. It can then be heated and slipped onto another motor shaft and the pulley re-installed with the spring and clips.
The photo Mooly sent from ebay is pretty much what I have however mine does not have the rear shaft support. I also have no knowledge if the pulley and adaptor are the same for an RD 11 and an RD 11s (they probably are). What I do know is that the Premotec motor I purchased is 300 RPM at 60Hz which is the same as the current motor and will work with the pulley I have. I just have to get the pulley adaptor off which based on the experience of someone on Canuck Audio Mart can be done. When I get around to doing (maybe in the next few weeks) I'll post whether or not it worked. I was also going to build a shaft support.