Several classes that were just different combinations of properties were removed and now you just set those properties appropriately to get the same effect.
The equivalent of a KActor (which was called PhysicsActor in UE4 previously I think) is just a StaticMeshActor with SimulatePhysics set to True on its StaticMeshComponent (and Mobility set to Movable - which happens when you enable Simulate Physics I believe).
BTW, an InterpActor is now a StaticMeshActor with Mobility set to Movable.