I would strongly recommend getting some chaos spawn bits rather than tyranid arms. IMO tyranid stuff is very identifiable as such, and the chaos spawn bits look much more... warpy; which is what you should be going for. Spawn kits come with an amazing over abundance of bits to customize with, meaning there are plenty of extras floating around. As for green stuff, you can't really go wrong.
Here are some I did myself last week using just a few parts leftover from the kit I mentioned. I don't know that these are the same wolves you are talking about, but I did have to pull goblins off their backs. They end up slightly taller and considerably more bulky than the old school metal khymera, which isn't bad as I made them each the "alpha" of their pack.
I have no idea how they compare to the new style kymera with the arms coming out of their back. GW has tended to increase the size of their models slightly with every new version so it wouldn't surprise me if the finecast ones were at least this size.
As for a paint scheme, I was going to try to imitate the warp with lots of purple and orange in sort of a nebula pattern. Sadly my imagination far outstrips my actual painting skill.