I have never done this specific conversion but looking at the pictures from games workshops website this is what i would do:
1. Grab the legs, torso front and torso backside with the most runes and pelts/fur on it together for the main body.
2. Sculpt power cables with green stuff on the torso representing the psychic hood
3. Decorate him up with lots of additional decoration parts and choose the coolest looking shoulders and head for him.
For creating a psychic hood you can look into this article:
http://fromthewarp.blogspot.de/2011/01/modeling-power-cables.html
There is also a nice example picture. It's not a space wolfs model but the principles are mostly the same. So the hardest part is probably the creation of the psychic hood power cables.