Here is what I came up with seems to work well for me. http://www.thingiverse.com/thing:861339
I have 3 versions of this, rev17, rev18 & rev19. Rev 18 is 1.5mm higher connection than rev17 & rev19 is another 1.3mm above rev18. If you are using that plastic pulley over the idler bearings, rev19 is probably the best of these 3 versions to use.