The unofficial background for Index Astartes: Iron Hands in the Dornian Heresy was written up and published by Bolter and Chainsword in late 2010. To cut a long story short: the Dornian Heresy is an alternate reality timeline where the loyalist and traitor legion's affiliations have been inverted. The Space Wolves shed blood and collect skulls for their Lord Khorne, whilst the World Eaters are the paragon of disciplined troops, loyal to the Emperor and on very friendly terms with the Emperor's Children legion. If you haven't read the alternate reality background, then I'd encourage you to do so -- it is remarkable in a large number of ways.
For the Iron Hands alternate history, Ferrus Manus slew Fulgrim and they went renegade. But they're not truly renegade ... they just have a bit of a different idea about how to combat chaos than the Emperor has. They want to upgrade (ascend?) humanity in to these metallic bodies they located on "tomb worlds" a while back. By doing so, they will remove emotions from the weak, fallible human bodies and deny chaos their food stuff: strong, nasty emotions! Perfectly logical, you see. Just like a machine.
In their research, they have mastered the phasing techonology of what was the necrons and adapted their Gauss weaponry. And they're still modifying their own bodies, replacing parts with more reliable mechanical bits. They're not ready to execute their master plan yet though. Only the very senior members of the Iron Hands have received the new metal bodies. Most of the battered legion's clans still retain their power armour (etc.).
For a test miniature, I used a standard space marine torso, legs and back pack and combined them with a chaos space marine shoulder pad, necron gauss weapon and hands / lower arm (left arm) and a vehicle upgrade bit on the top of the back pack to give the suggestion of advanced and beyond-the-inert-imperium technology. The head was chosen to be the bionic human head from the space marine kit. I was toying with using a necron head, but the bionic head was much better suited to the background and the miniature. The painting was relatively straight forward, with a standard approach to painting black, with silver edging around the shoulders. I tried to add some green reflection from the gauss barrel on to the left forearm and the left hand side of the chest. I'm not entirely convinced it works, but it's the first time I've thought about doing such an approach. Finally, the base is one of the resin bases that I painted up some months earlier.