Erm its not THAT complicated, hes showing the steps to how he made his, Hes taken a inquisitor scale marine helmet and put it where the sarcofagus on a normal dread is and greenstuffed a knightmask on it to make his which is the 4th picture, the first, second and third pictures are all from the GW online store. Sheesh.
I think its saying I is the helmet tha is isn the first dreadnought, the powerfist can turn on that one, The 2nd dreadnought (U.M) has a converted helmet in there, and the Iron warriors dreadnought has the last helmet in it...I think..