Dr. Bussard says that the number of edges meeting at any vertex must be an even number for optimum operation of the magnetic grid.
Here are some candidate solids you can play with
The Rhombitruncated Cubeoctahedron
Or you can go to the main page and look at different solids. The indivildual geometry pages I have given are Java applets. If that doesn't work for you the main page also has them in VRML.