From Mustangmotorsport.com:
"Next up is the subject of anti-moan brackets. I had someone send me some brackets that they claimed were from a 99GT. When I tried to install them, I noticed they were too short in length if I tried to mount the U-bolt thru the shock mounting bracket. If I placed the U-bolt on the outside of the shock mounting bracket, the anti-moans didn't quite fit, but I could have bent them slightly to make them fit. I have seen pics of people making these 99-up brackets fit with some force, but I decided to get rid of them and buy some correct length 94-98 anti-moan brackets which fit perfect. The 99-up unit is on the left, and the sn95 is on the right."
http://www.mustangmotorsport.com/images/5lug/99antimoan.JPG
http://www.mustangmotorsport.com/images/5lug/sn95antimoan.JPG
I guess there is a slight difference in length?
I used a pair off a 94 and they fir perfectly.