Summary

Modified http://www.thingiverse.com/thing:12609 to use a Misumi leadscrew MTSSR8 nut and self-aligning bronze bearings or Makerslide.
For a x-carriage see http://www.thingiverse.com/thing:245688

Instructions

Get all of the parts from http://www.thingiverse.com/thing:12609
The scad file uses x-bracket_1off.stl and zClamp_4off.stl. See the notes in the file for more info.
The scad file is somewhat parametric.
Print at least one of SimpleVX-ZClamp.stl for the motor mount. Three of the SimpleVX-ZClamp2.stl. Using a brim, support is not needed if you have your bridging set correctly.
Use one 625 bearing, 2 regular washers, 2 fender washers on a 50mm 5mm screw for the idler mounted in the center hole with two of the standard wheel spacers spacing the bearing from the SimpleVX-ZClamp2.stl.
SimpleVX-ZClamps mount on the non-rail side of the makerslide using two screws. The motor side uses two 35mm 5mm screws, and idler non-bearing screw uses a 25mm 5mm screw.

Vertical X axis