Appears to me that the inner side of the switch is a 360 degree little sprocket. Almost like an 8 mm ratcheting box wrench sprocket. It slides on right until I get to the flats of the selector shaft and stops stone cold.

 

Which side rests on the transmission ? The black or metal side ?

 

Your XYZ switch hub should look like the one in the picture I've attached. You can see the flat section on the bottom of the hub as it appears in the picture. That needs to be line up with the lower flat on the selector shaft. It should slide on easily if it's lined up correctly.

 

Raider1974, can you share any update with us please?