This is rather cool. Here is a new set of rules for your Imperial Knights.
via the Warhammer Community
https://www.warhammer-community.com/2019/01/14/14th-jan-the-horus-heresy-new-imperial-knights-rulesgw-homepage-post-1/
If you’re a fan of the Age of Darkness, we’ve got some great news for you – especially if you enjoy delivering death from the comfort of a Throne Mechanicum! The studio has produced some new rules to enable you to use both patterns of Armiger-class Imperial Knights as well as the towering Castellan and Valiant patterns of Dominus-class Knights in your games of the Horus Heresy. Cool huh?
After all, the Imperial Knights pre-date the Imperium and the tragic events of the Horus Heresy, so these mighty war machines would certainly have marched to war along with their fellow Knights. These new rules will enable you to do just that!
You can download the free rules PDFs by clicking on the icons below: