I am pretty sure that if you built one (whichever one you fancied) exactly as it comes out of the kit, you could have the fancy top doohicky left over for the other one, plus a body and enough arms to build one crew member for that (there are two acolytes and one wizard) as well as various "specific" detailing bitz.
You would then just need some sort of body or other "thing" to make the cart itself. I am kitbashing and scratch-building a cart for my Hurricanum, and am mounting my Lumminark Archimedes mirror on a giant bronze bull (scratch-built) so they fit better with my army's fluff, but I considered getting a plastic toy Chimera (from JoAnn fabrics of all places - $13!) and using that for the purpose.
I think there are lots of options; mount the device on a large monster of some kind (toys are your friends!) or get a cart / wagon of some kind.
With judicious use of plasticard, I think you could replace the "base plate" of the cart with a sheet of plasticard and put on different (less-decorated) wheels and put the body on there. The base plate is detailed, but not really seen on the model once assembled.
Then, you could use the decorated baseplate and wheels on the other cart, and build a frame / support out of sprue and plasticard to lift the top doohicky up a little (to give it some height). A different animal or animals to pull it, and the job's a good 'un. I think you could very easily get two lovely models out of a single kit, some spares and a bit of thought.
Of course, people will have noticed I will have most of the body of one of these things spare . . . make me an offer