I think you are on the right track. The key will be having a good robust way of transferring the thrust forces from the ram to the hull so the design of the bracket is important. Remember: Nothing too strong ever breaks!
it is normally considered best practice to have the autopilot drive attach to the rudder shaft with a tiller arm separate from the normal steering system. Thus is done for two reasons. It avoids needing to add a hole in the existing structure and thereby weakening it, and in the highly unlike event the existing quadrant was to fail or come loose, the autopilot is a completely redundant system.
