I built the z-motor-bracket and the last corner bracket out of a single block of wood. This makes it much easier to build. It took a lot of work to figure out where everything went. I ended up drawing it out on graphing paper.
The block is 74mm x 74mm and 1.5 inch thick. Before I drilled any holes I marked a large circle with a radius of 20 mm in the center. (x, y) center is (37, 37).
I drilled an 8.4 mm hole through the block at (x, z) of (24, 23) and another at (y, z) of (24, 9). These two holes are part of the corner bracket and hold the x and y rods.
On the top there is an 8.4 mm hole that goes through the block at (x, y) of (11, 11). This will hold the z rod. I also made holes at (11, 37) and (37, 11) so that I would match the other corner brackets, but they aren’t actually needed.
There is another hole through the top that I made with an 8.4 mm bit. This is at (37, 37). After getting the motor on, I decided this would be better with a 10 mm bit, but I don’t want to take it apart to redrill it.
The remaining holes on the top are used to mount the actual motor. I used a 5.4 mm bit from the top to start them. This has to go at least 5 mm deep. The locations of these holes in (x, y) is (6.8, 23), (23, 67.2), (51, 6.8), (67.2, 51). After that, I flipped the block over and drilled 10 mm holes in the same positions but stopped 5 mm from the top of the block. This creates 4 holes with a lip on them.
Finally, to make it easier to put in the nuts, I used my side-cutting bit to clear the area between the 10 mm holes and the sides, again stopping 5 mm from the top.
The final step is to clear the circle I marked earlier. I set the side cutting bit to cut 2 mm deep and cleared it. A quick check with a motor verified that it fit and the holes lined up.