I have nearly finished my Warsmith on a Juggernaut of Khorne (initial post here). I love the sculpt of the model, in fact that is the reason I got it (actually my wonderful wife gave it to me last Christmas!). I did very little modification to the model itself to pull it into the 40k universe, but by the very nature of Chaos, it can easy pass off as archaic MkI, a bit twisted by the warp.
I did the base coat just I did any of my normal Iron Warriors: Mithril Silver and Shining Gold, Devlan Mud and Badab Black wash. The metals were then re-dry brushed before washing with Baal Red and Ogryn Flesh.
Still left to do is the power weapon, shoulder plate XIV, pouches, and the base.