Here is a sequence of photos that shows how the router bridge adapter board is fixed and populated with all the required components.

First photo shows Y axel handle (on the left), which is connect to the Y axel ball screw, on the back of the router bridge. We can also see (on the right) the Y axel slider, that will support all the Z axel structure and spindle motor weight.

Second photo shows the fixing board secured by 3 of 4 screws, that hold it in place, against the Y axel slider.

Third photo shows the new ball screw nut assembly, which includes a support fixture to hold the ball screw nut at 90 degrees angle.

The fourth photo shows how movement is transmitted from the Y axel handle into the fixing board, that is securely attached to the Y axel slider. To transfer power 3 screws are used, being one longer than the others, so that it can go through the board and reach the Y slider, behind it.

Finally we secure the Z Slider, using 4 screws, but a thick clear acrylic is used to make the slider pop out, so that it will correctly align with Z ball screw center, passing in previously secured Z ball screw nut.
The Z axel holding structure will be aligned using a rail guide that goes through the Z axis slider.