Certified GKH Gardening Expert
I don't think that I would recommend growth inhibitors in this case. You would need to obtain the correct chemicals specific to the tree, while trying to prevent it from coming in contact with specimens nearby. I recommend growth inhibitors in very controlled situations.
In your case, This extraordinarily large tree might be best removed by a professional in your area. You could try your local extension service. They may have a few suggestions for people that can help you to remove the tree in your area.