I have finished a new version with some (hopefully) useful refinements http://www.thingiverse.com/thing:652810
I have taken a wades extruder, redrawn it using Designspark Mechanical and added some of my own ideas. I have:
1) Changed the way the motor mounts
2) Made the nuts accessible
3) Changed the mounting of the 608 bearings so you can remove the bearings easily
4) Changed round holes to hexagonal
I may put the idler hinge back in but I wanted to try it as is, first.
I will upload the source files in a few days when I have finished tidying them up.