I did this conversion recently. Basically it's an Emperor's Champion for my Dark Angels, but the joke is that he was made not using even a single bit of the GW's EC model - all parts used (well, almost all...) come from the Tactical Squad and the conversion is pretty simple too.
The finished model can be seen in these places:
Mirror Gallery
Oh, and there is also a complete instruction on converting him, have fun trying. :lol: