The lower control arm mount on a mustang body is located at the bottom of the uni-body subframe rail. There is no support for it when it the car launches and the lower control arm pushes forward on it.
Here is the lower control arm support / frame connector that I fabricated for the CobraJet.
Here is the driver side lower control arm support installed on the body, ready to weld.
A close up of how the enclosure fits over the lower control arm mount.