Still making some progress if a bit slow. I've now fettled the column dovetails (they weren't too bad really) and made the same mod to the gib screws as for the X and Y. It all works smoothly now.

Checked the alignment of the spindle to the column:
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.. found the spindle is parallel to thee column within 2 thou over 8 in. However the head is skewed giving 20 thou variation in 8 in when measured as above. I'll have to separate the two head castings and re-align.

Russell.