When the motors came in, the X,Y axes motor mount brackets could be made and fitted to their respective bearing blocks and motors. Alignment of the motor shaft with the ball screw shaft is critical, and I wanted the couplings (Oldhams) with as little misalignment as possible. To align the motor shaft with bearing center when marking the holes for the motor mount brackets, I made a coupling shaft from 1/2" CRS, with a 10mm OD section and a sectoin supporting a ¼” hole in the opposite end to allow engaging the motor shaft and the bearing block together.
Then, to get the proper length for the motor brackets, the bearing block was assembled onto the ball screw and the coupler installed. The other half of the coupler was installed on the motor shaft and the two were mated together. Careful measurements of the spacing were then taken and the bracket pieces cut to length (errors here should be on making the bracket too long; too short and there is no way to correct it). The motor holes were then transferred to the brackets and the clearance holes drilled through. Unfortunately my design resulted in some clearance issues between the motor mount bottom and some of the bearing cover bolts in some places so relief was milled into the ends of the brackets to clear some of the bearing lid bolt heads, but eventually everything fit. Then, the ball screw was removed from the bearing, and the alignment coupling shaft put int the bearing and slid onto the motor shaft. The drilled motor brackets were put into position and the motor pulled tight and a transfer punch inserted through the mount bracket to mark the bearing block. I did one side at a time, drilling and tapping the 10-24 holes into the bearing block. With one side in place, the other side went quickly. The final thing to do was to bolt everything together and identify any areas that needed to be corrected (remember the .050 oversize to allow for some final machining to make things look nice).
The first two pictures show the coupling shaft fitted on the X-axis bearing and motor brackets, the last two pictures are the completed motor/bearing assemblies.