[NiteRabbit]

I usually shy away from creating loyalist versions of post-Heresy Chaos Legions because of the major complications involved. However, if you want to go ahead with it, you'd have to be prepared to explain several questions. First, how did they avoid being purged by the Inquisition in the aftermath of the Heresy? Second, where do they get their Geneseed and supplies from, since all traces of Horus (including the clone) were eliminated by Abaddon after he arrived at the Eye of Terror. Third, you need to go for the usual stuff like Combat Doctrine, Beliefs, Organization, Homeworld, etc. All that fun stuff.

Good luck with that.