quick dig about and got the kliktronic off an old sidecar i had [the flat-bed one] last night.
need to have a work out of angle of the dangle but this is pretty close i think. should be an easy fit. just a tab on the frame. they are just an electromagnet so pretty bulletproof, the way the linkage was looking like it would have to go round corners, past frame tubes etc this is more reliable then a heath robinson mechanical setup.