will be available when you can order on NN store. Not far to go.
One question to get things right: What do you like to use? New foot plate, RD4 on top, and then? Using RD4 as shown in Nick's picture, will offer the normal 3'8" female, or with the additional 3/8"to 1/4" screw as another option.
Using a Fanotec pole, this can be added to the RD4 with the included 3/8 screw. Sorry I do not understand the RD16 connection.