FYI. I purchased stock UCAs, LCAs and swaybar from a 2003 GT for $20 to replace my 1990's worn out parts. After a couple hours, I had them swapped out and they worked 100%, even the stock '90 sway bar bolted right up. The LCAs were physically identical and I could only guess that the 1999+ Stangs must have a mounting spot for ABS, etc.
Vic
Vic