So i went a different route. With a bit of hack and slash, I've managed to get my carnifex to lay down and use his front claws as another set of feet.
I used the chopped down crushing claws because I think that they would be a lot more stable to walk on than Scything Tallons.
I still need to do quite a bit of GSing, and add the "Brood Sac" from the Stranglethorn Cannon, but She's getting there.
Here are some more pics:
Any thoughts/ criticisms are gladly welcomed.
Thanks - Stephen