Silyavsky thanks for the hearts :) feeling much better now.

You and Eddy are absolutely right in your assumption. The design has changed since than. Instead of the 50x100 pieces I have used 100x100 ones all round and now the vertical bit is all the way to the back.Originally I have brought it forward to leave access to the HIWIN blocks but with the 100x100 profile it is no longer necessary.
It looks like this at the moment:
Click image for larger version.  Name: P_006.jpg  Views: 433  Size: 77.6 KB  ID: 13152

I have tried to design it in a way to have the blocks fixed and the rail moving, but the gentry become a lot taller.
The reason for that is the fact that the lowest position of the spindle is different from what you have seen.
You can see it better in the following picture.
Click image for larger version.  Name: P_007.jpg  Views: 451  Size: 99.8 KB  ID: 13154

Thanks again Silyavsky and Eddy.