3d taxi voronoi mesh creation - cutting/combining polygons help/advice please

[Chronocide]

I made this here debug testbed with PyOpenGL to work out how to construct a perpendicular plane in taxicab metric, aka manhattan. 
Any advice in constructing voronoi region meshes with these perpendicular poly planes would be welcome. I am looking into pycsg, but I don't think it's ideal for this task.