Question Best way to link between a GameObject and a Entity for Hybrid scenarios

I have a custom scenario where one GameObject has 100-200 MeshRenders + LODs as children. I moved them to entities with a root parent entity. What would be the optimal way to link between that parent GameObject transform position and the parent Entity of those entities in terms of position/rotation?

I can't fully convert all GameObjects to entities. Is there a helper, or should I implement a custom System?