The gods of eBay have smiled upon me and I have all the bits required to start putting my Zoat Devastator together. As perviously mentioned, this huge thing will be a proxy for the Tyranid Tyrannofex. As you can see it really fills up the large oval base... and then some!
I need to do some work with the weapon to ensure it fits the hand - it will be holding the cannon rather than it being a biomorph. It seems as if the Ghorgon torso will fit quite neatly into the Carnosaur body, with only a little sawing and green stuff required. Other than that it should be tinkering around the edges. Exciting stuff!