When I used to work as a mechanic, it was rare to find worn lower ball joints on a car with a "Mustang" type front suspension. It seems that the suspension design, where the spring is above the upper control arm, puts most of the load on the upper ball joint. Conversely, in cars with the spring in the conventional location between the control arms, the lower ball joints seemed to see more wear. Maybe someone with an engineering background can shed a bit more light on the subject. I'm just speaking from personal experience. You know, I've been getting some stuff from Rock Auto and have been very happy with the parts, the prices and delivery. I shy away from Auto Zone and the other chains. We are lucky to have an "old time" traditional independent parts store that I deal with most of the time.