I took a chance on a used ground ballscrew complete with bearing blocks. Looks and feels really good, can't wait to see how it performs. The plan is to use it for the X2 Z.
Which of these 2 ideas looks more feasible. The first is the Syil approach as shown here. http://www.jeffalbro.net/cnc/syil-x2/syil-x2-03-800.jpg
The other is a side mounted approach as shown in the attachment. You'll have to imagine the screw ~1/2" further rearward and a heavy flat plate bolted to the ballnut to move the spindle.
The side mount is simpler to make but I suspect Syil went through the extra work for a good reason.