The assembly guide on instructable is a bit garbled in section 9. It refers to left where it means right several times, and it doesn't have the details of the subassemblies in the way that the previous section does.
Left/right confusion has been fixed, and this section isn't quite as detailed because it is very very similar to the previous step, however I belive there are supposed to be annotations on the idler pulley sub-assemblies. I will look into that. Thanks!