You will need the entire lower control arm, which comes with a new ball joint and new bushings. To replace just the lower ball joint, you would have to press out the old one, and press in the new one.
The lower shock bolt can be a pain, so read up on old posts about that.
Steve - TCCoA member
2003 Crown Vic LX Sport
1995 T-Bird LX 4.6 retired at 247,888 miles
Thanks for the ride !