The first thing I had to do was cut the head off the bust and create a new neck in Blender. Then I scaled the head to match a typical 28mm model head. I sent this off to Shapeways. What came back was actually slightly too small. The problem with small parts is that half a mm is a lot on a head that's 4mm wide.
I really need to buy a better micrometer, with a digital read out. The one I have is a really basic mechanical model. This is the key tip when working with Shapeways. Triple check your measurements. Then measure again.