The stock suspension on a Fox body was designed in the late '70s. Perhaps it was adequate at the time, but we demand more from these cars now on both the street and track. Whiteline rear upper control arms are a big improvement over the stamped steel units from Ford.
One of the biggest improvement with these control arms are the bushings. The factory rubber bushings are soft which can translate to binding issues, wheel hop, and generally offer too much compliance when trying to put power down. On the other side of the spectrum, control arms with polyurethane bushings don't offer any articulation, okay for a drag car, not one that you plan to autocross or bring to the track.
Whiteline control arms use their patented Max-C dual durometer bushing that does offers articulation, and unlike an all metal spherical are going maintenance free and whisper quiet. No rod end to wear out, perfect for a street car that sees some track time.