Ive managed to finish my honsou (more or less - just got bits and bobs to add, but the basics are done).... heres what I used:
Helmet - bare head with bionic eye from the BaC MkIV sprew. I put a tiny bit of glue on his face and jabbed it with an Xacto to make it look scarred.
Left Arm - Chaos marauder arm. Tried with a catachan arm, but it looked shit to be honest, just all out of proportion.
Right Shoulder / Arm - Black templar power sword arm (with the chains) and cut the sword off.
Chest - Iron warriors old GW upgrade torso. Its chaos enough, but not TOO chaosy.
Waist - Legs from the BaC set, but added some spikes to it. The chaos standard legs just looked a bit naff.
Weapons - I kitted him out with BaC combi melta, and the DV chosen axe head with a length of 1.5mm rod for the handle. Also added a spike to the handle end as i couldnt think of a better way to finish it. I considered giving him a standard bolter, but decided that actually he would look better with a combi.
I need to add melta bombs to him and some grenades/pouches etc, but he's basically done. Will post pics when ive finished him up.
I am struggling with matching rules to the model though. He has no mark, but has got combat familiar. Think i might add a servo arm to the CSM backpack or something, but that doesnt quite tie up with the novels. Havent decided if i care enough yet; will be painting it separate anyway so will decide when i have finished painting. Ive found it difficult to match the fluff with the model rules. He's essentially a barebones CMS lord, but I'm running him with a unit of chosen to represent the newborn and grendel and the others who attended Calth during his latest jaunt.
Hope that helps.