I did one for Tzeentch but it appears the pics were a casualty of the last annual board meltdown (just kidding, CS, you know I love you

).
Briefly...
Replaced the sensorium and towers with a large central obelisk and smaller surrounding obelisks. The front corners of the carapace have Warmaster Liche Kings (the ones on the thrones) on each. I used some 28mm canopic jars and a bunch of Blood Bowl Khemri shoulder pads (shaped like scarabs) to fill in and decorate the carapace
The head was replaced with one of the t-visor heads from a Warlord titan. The headdress from a 40K Ahriman provided horns and the dangly bits, so the overall size and shape was comparable to the original Impy head.
The feet were mounted on washers, which were then textured to look like flying discs. Those were on top of a couple of flying bases which were hidden under the discs, so it looks like it's hovering a few feet above the ground.
Weapons were in-process. I'd cobbled some stuff together but I didn't like it.
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I've been debating on scrapping it and starting from a new concept keeping it in line with the Silver Tower theme. The overall look would be almost like it was encrusted with silver tower "barnacles" growing on it.
Carapace - Keep the big, central obelisk. Add a floating, flaming eye, a la Sauron over it. Build up the rest of the carapace like Silver Towers. Have a few towers clinging to the edge and hanging down underneath the carapace as well.
Bastions - Re-face them to look like a set of towers rather than a single structure. Have a couple sticking up in front of the knee joints, or possibly attached directly to the front of the joints.
Weapons - For one of them, a hand/powerfist holding a giant flame, possibly ready to throw it. For the other a standard chaos-ified weapon. Have a tower or two sprouting from the shoulder(s) or spine of the weapon.
Head - Remove and replace with a structure of more towers that's only vaguely head-shaped. It doesn't need a head to see. It has a giant, flaming eye. Alternately, I thought about using the original Imperator head and having towers sprouting from the eyes like they were blind and crusted over, maybe with a beard of hanging towers as well.