Talking about blurry

I've started to consider the z part now, but, as usual there is something wrong.
In (http://www.reprap.org/bin/view/Main/McWire_Cartesian_Bot_1_2) the BOM for the z part states 24 for the rails (ie 12 inches each). Mine are cut to 13 " each, as per the 'Cut aluminium rails to length' instructions.
The so-called vertical base appears to be the same size as all the stages throughout the webpage.
However, if I put my z rails up and down a portrait oriented vertical base (being 11 " tall as per the 'Acrylic cutouts' section) the size of the aluminium angle means that it doesn't fit over the MDF - it catches the edge, whereas the McWire picture shows a large gap bottom and top. My aluminium angle is 3 cm deep whereas the McWire's is 1.5 ", which is actually larger. So the problem is not due to the size difference of the angle.
Hmmm.
Is the vertical base actually landscape? It really doesn't look like it, even when I zoom right in to the http://www.flickr.com/photos/hoeken/2293533001/sizes/o/ Flickr picture.

I can only assume that the rails need to be longer. But how much longer?
Maths guess: 11 " vertical base + 1.5 " angle + 1.5 " other angle + gap = ~15 "

Now, I've used 94 " of my three lots of 1 metre u-shaped channels (117 ") so there isn't enough left (maximum 13 ") to re-do these lengths. So now what? Does this mean the z-stage doesn't have its full range of movement?

For now I shall have to turn the vertical base around to landscape orientation, stick with 13 " rails, and probably have to cut a new z threaded rod to 12 " because I've nicked its intended one for the y-stage (instead of the 18 " one I'd cut for that).
I may have to buy some new rail and cut a new board (unless the holes aren't in inconvenient positions when turned around) if I need a bigger range of movement. I guess this will have a knock-on effect on the software settings, too.