The Ferguson system was pretty crude. The cars also gained the company's experimental anti-skid braking setup, a mechanical forerunner to the ABS of today.
Though performance and handling were improved, the modifications were too expensive and Ford ultimately gave up on the whole idea.
Ferguson continued to test their technology on a whole range of cars, including more Mustangs, and the system later found its way into the Jensen FF, the first production car offered with AWD.
Officially, there were two prototypes, plus a couple 1969 fastbacks, including one built for a Ferguson executive with a 428