This holds the v1 power shutoff switch on top of the left YZ plate with the mount holes that are prebaked into the YZ plates.
The author remixed this model.
just used the segment in front of the z screw before the z endstop holder that has the bolt holes and contour to match the top. Hollowed it out, widened it up to fit the estop, put in a countersink hole for the mushroom button and a cover to hide the side.