Dear Henrik, 
We studied your suggestion about the use of Rigid coupling for the ATFD.   Refer 2 attachments for 2 options for the coupling.  
Option-I is based on your rigid coupling design while the Option-II is based on our roller chain type coupling design.   Please compare simplicity in arrangements in both the options and let us know your choice.  We tried to elaborate the overall height requirement, ease of overall handling, weights of the assemblies to handle while maintenance etc.  We felt that our design is easy to handle.  Please review