So here would be my suggestion for the smaller Bull Centaurs in WAP 8th edition.
Basically it’s their stats/equip from WAP 9th, but like regular Chaos Warriors or Renders they don’t swap their shields for another weapon but can add it. Most notably is the change from troop type cavalry to war beast. It might be nitpicky, but, well, they are not a mounted unit, they are essentially beasts (like Renders are monstrous beast and not monstrous cavalry). But that also has some real-game implications: Since they are not mounted, Bull Centaurs (like Renders) can parry. They also don’t fail dangerous terrain tests on 1-2, only on 1, which makes sense, since the reason for the 1-2 is the increased difficulty of handling a mount, which Bull Centaurs obviously don’t have. However, Bull Centaurs are still quite large, easily bigger than a horse, which would raise some questions regarding (thunder)stomp, where war beasts can be stomped but cavalry cannot. Also for combined units and look out sir, they should be more like cavalry. I therefore just gave them a special rule for these instances. It might seem to be cherry picking, but I honestly believe Bull Centaurs should have the best of both worlds here. Accordingly, I upped their points. What do you all think? Different stats, equipment or rules? Maybe even 22 points?