MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
The diamondesque shaped piece with four holes that mounts on makes up the second half of the Y_carriage part. You can see it near-center on your second photo. I grabbed a capture of it with snip-it (I'm old school) and highlighted it in yellow. Maybe I just missed it in the file list. I can print out the other half and draw up its made in SolidWorks, it's not a big deal and then I'll have it.