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.
It may be difficult to follow the names of the parts and how they interact together coming into it new -- reading through the build manual will probably help with that. Also, the part files are named and the OnShape document I linked has the parts named. It probably is a good idea to build it at 3:1 first before attempting to scale it down, though.
Btw, if you want to understand the device more or are just plain fascinated with it (like me), I highly recommend the Curta Calculator poster (http://www.vcalc.net/cu.htm). It has an exploded view of the Curta and most of the parts are labeled. I wish I had that when I was getting started. The names of most of my parts are based on the google translation from the German part name listed on the engineering drawings which aren't always super accurate.