Hi Michael,
When you break the Hit Result around 1:52, you can see there’s something called Hit Item. For InstancedStaticMeshes that returns the index of the instance that was hit. That should be much easier than trying to find it based on the transform!
Version 4.9 adds some more blueprint functionality to allow you to find instances overlapping spheres, and also to allow you to blueprint the component class used by the foliage tool.
Cheers