This modification is called the Half truncated cube for now. So far, myself and the gang on the forum can't find a classification for the polyhedron. Basically, instead of all corners being truncated, only 4 of them are, which results in a very attractive twisty mod.
This mod is not the sort you would mold and cast for (although you could). This one is best use to use a bench grinder and sand the pieces. A lengthy process but then, it would take longer to cast the entire 20 pieces needed.
Filling The Cubies With Polyester Resin
For the best results with this mod, I used a SevenTowns Cube. The first step was to use black polyester resin (yes it does have it's uses), as a cheap filler, to fill the hollow of all 12 edge pieces, and four of the corner pieces. The other four stayed as they were, because they were not be altered. The reason they are to be filled, is that all the pieces need to be subjected to the grinder in order to shave off a section. Once done, they will assemble into a rough half truncated cube.
To remove the caps on the SevenTowns corner cubies, I drill a hole into the cap and use a hook to pop it out. It won't be used again anyway. For edges, it's a simple matter of pouring. This technique was first shown on the Puzzle reconstruction site. Take note, that if you were to pour the polyester resin straight into the edge piece while it was on it's back, the liquid would come out the lower end. Use blutack or putty to balance the edge pieces on their spine. The polyester resin flow must fill up level with the back wall of the edge cube at least, as you can see in the photo on the left.
With regards to the corner piece, after removing the bottom caps, you can simply turn them over and pour straight in. Here again, you MUST fill resin to the top, level with the opening. Too much will leave a convex arc at the bottom of your piece which will hamper movement, and too little will leave a concave which will look dreadful when the grinding process is finished. So try to get it 100% flush.