Well, had to make another Herald of Tzeentch on a Chariot, so I tried to take some in-process pics to write up a short guide. Let me know if you like this...if the response is good, I may do more.
Parts List:
2 Screamers of Tzeentch
Sorcerer of Tzeentch (WFB Chaos)
Disc from the Tzeentch Lord (WFB Chaos)
About 10" of jewelery chain & 7 jump rings (you can get this from most hobby/craft stores)
3 Flying base stands (the shorter, the better)
1 Chariot-sized base (100mm x 50mm)
Tools Needed:
A needle-nose plier-like tool (I use surgical clamps, actually)
Pin Vise
Dremel or other hobby tool (optional)
Glue, etc.
Hobby Clippers
Things also become MUCH easier and sturdy if you liberally pin nearly everything. Up to you, but I highly suggest that you pin all joints/joins.
STEP 1:
You want to start by doing all the normal pre-assembly work - cleaning off flash, filing, etc. Definitely dry-fit all the screamer parts (body/tail) together to make sure that they match up.
STEP 2:
Time to use that pin vise. (A Dremel or other powered drill will make this a lot easier/quicker). Drill a hole in each of the three large spikes (from the Disc of Tzeentch), and in each back of each wing of the two screamers.

At this time, I also pre-drilled the disc and the sorcerer for later pinning.
STEP 3:
Time to attach the chains to the screamers. Open the jump rings, so you can thread the jump ring into the holes drilled into the screamers' wings. Then thread the jump wing into the chain, and close the jump ring. You want about 2.5" - 3" of chain hanging off the end of the screamer.
Repeat for all four holes that you drilled into the screamers wings. It doesn't matter if the chain lengths are uneven, because you'll be evening them up later. Now's also a good time to attach the tails to the screamers.
STEP 4:
Assemble the sorcerer (your future herald) to the disc, and assemble the spikes to the disc.
STEP 5:
Now its time to attach the screamers to the disc. Start with the inside chain of one screamer, and thread the chain through the jump ring mounted on the center spike. Using the inside chain of the other screamer, thread the chain through the same jump ring.
Before closing the jump ring, make sure that the length on each chain is the same. Once you're satisfied to the length of the inside chains, close the center jump ring.
Now attach the outside chains to the outside spike. You want to attach the outside chains so that when the chains are pulled taut, the screamers are lined up and look like they're pulling the disc, as shown in the picture below.
STEP 6:
Clean up the chain by clipping off any excess chain. Make sure you're clipping the right links!
STEP 7:
Time to mount the chariot on the base. Start with the disc - its the heaviest, and its position will determine where the screamers go. I used the tallest of the flying stands to mount the disc on, and pinned the disc to the stand for extra strength.
Drill a hole into the base where you want the disc to go, and mount the disc on the base.
STEP 8:
Mount the shorter flying stands on each screamer, and then mount them onto the base as well. If you want to give the model the illusion of movement, you want the chain to be a taut as possible, so mount the screamers as far forward as possible.