Hopefully these two images are enough to portray what has to happen.
The pivot ball of the shifter needs the white and black ring around it, then that structure needs to be clamped in between the larger shifter base and and hold-down piece, which screws down onto the base. For that to happen, the white and black ring and the hold-down piece both have to get between the pivot ball and the reverse-lock part of the shifter.
The only way I can see to get them there is to remove the pin in the reverse-lock part and slide that part up and off. But, the pin does not move easily and I don't want to risk breaking it if I am wrong.
Thanks guys.