Perhaps I was a bit naive here, but I took a rather more simple-minded approach to ballscrew alignment. Both ballscrew bearing blocks were clamped to adjustable mounts that allowed me to move the bearing up and down, left and right. I left the clamp bolts loose enough to allow the bearing block to move, then wound the ballnut attached to the carriage to that end of the ballscrew. Clamp bearing block in place. Ditto at other end - allow ballscrew to locate bearing block. Tighten. Job done. Didn't need to blow the dust off my DTI...