Anyways, I am posting mine here simply to show how I go about doing my version of this popular conversion.
Above you can see, I take the back half of a Chaos Warrior Torso, and make a mess of it with my Dremel. The grinder bit I have attached is the perfect tool for this job. I also cut the top half of the front of the Chaos Warrior apart from his legs (I like the full front torso, but I like the look the Marine legs give with this conversion better)
After I'm finished making a mess of things, I clean it up with some Green Stuff. I am not too concerned with how it looks at this point, I'm just trying to smooth it out a bit. Most of it will be covered with the rest of the model anyway.
I then attach the front, I should note here that I hollowed out the back of the front piece, as well as hollowed out the waist area of the back piece with the Dremel, this is to allow for a better fit for the legs. I also fill in the gaps between the front and back torso pieces with a little Green Stuff.
Using a small ball of Green Stuff, I put it on top of the legs of the Marine, then using my sculpting tool, I make a small Wolf Pelt around the waist. This fills in any gaps between the torso and legs, I then use floral wire as my pins for the arms.
The above two photos show the army attachment, the gap on the right arm will be filled with Green Stuff, I'll also bulk out the shoulder pad a bit.
I attached the Plasma gun, and the head, I had to use some Green Stuff here as well in order to raise the head to a level that looked and fit well with the torso.
I added a few bits around the waist where I didn't like the join, to hide any deficiencies, and here he is ready for his base.
I hope you all enjoyed this, please if you have any tips or comments for me, then fire away!