This part was also posted on Thingiverse by Robert Jackson R2Maker, you can find it at http://www.thingiverse.com/thing:55991
Those plans are currently (04/14) being updated based on recent scans so I expect that there will be updates eventually.
You can download models in STEP AP203 (.stp) format in English (inch) units as well as in 3D.pdf format: click here.
I've added a lens to this version of the 3D model. The R2BC plans call for a half sphere (cabachon) lens and that is what's modeled here.
You can download models in STEP AP203 (.stp) format in English (inch) units as well as in 3D.pdf format: click here.