Well, I made my 3x3 from your video (I believe), I'm just a little confused as to the mechanics of making it a 4x4. I don't have a 4x4 and am not intimately familiar with the mechanism.
the Rubiks 4x4x4 mechanism would work perfectly, like just truncating and filling.
The Eastsheen mechanism needs either a very hard filling method or plastic sheeting.
The internal 4x4x4 pieces will not be affected.