Attached are the geomteric shapes shown in the image. The attached ZIP file includes a STEP file for those of you not running Creo 2.0.
Do with them as you will. I opted to change the size of the stem and cube to account for common sizes and remain 100" between centeres. Now the Strut is 60" and the cube is 40". This means that all the geometries have a 20" distance from the face to the center.
I will admit that the Rhombic Dodecahedron was a surprise creation.
Some of the more adventurous among you will find some interesting techniques in the files. But in general, this was done to the best of my ability to manage a common center within a single part file and remain fully parametric for each model. I learned a lot about how to drive sketches to obtain my requirements. See the initial sketches inside the Icosaherdron.
Disclaimer: I am not a mathmatician! I depend on parametric sketches to drive my models. Nothing is simply rounded. Everything is driven by pure geometric relationships.