After a lot of time being partly build (or un-built in the case of the unit champion) I've got around to finishing these guys off.
A major advancement in the speed of finishing my models Army Painter coloured spray (available at hobby stores and at a discount from everyone's favourite Plaguebearer), Ultramarine Blue. This had sped up the process of painting the main colour on my models, as it cuts out at least three layers, and goes on a lot smoother. It is a little bit brighter than my other models, but with a bit of darkening with shades, and applying the other colours, its a lot less noticeable: you would have to spend some time telling the difference.
The conversions on these guys were fairly straightforward. The wing-like fairings of the standard Dark Vengeance bikes were replaced with the fins from Warp Talon jump packs, to give a more chaotic feel. The torsos are from Chaos Space Marines and Possessed marines, and the heads are from Thousand Sons. On two of the bikes, a small piece of Chaos brass etch was added to the back fender.
I did encounter issues with adding the power packs, which were partially blocked by the bikes' seats. In the end, I trimmed some vents off the power packs and a bit of the seat, so they could be added to the models.
I've armed by champion with a power maul. This piece was a normal maul taken from the Forsaken box, which happens to have a ton of cool and useful parts.
The next stage for these guys is to add even more bikes; to bring the unit up to 7-10. I plan to add two more Plasma Gunners, and an icon bearer. I'm deciding between styles, either normal Chaos bikes, Imperial bikes, or the new Forgeworld ones. If anyone is selling some bikes cheap though I'll be interested, contact me if you are.