new struts
 

I just purchased a pair of KYB GR-2 struts, and was wondering when I take the old ones out do I need to rent a spring compressor or do I not even have to bother with the springs when changing the struts.

The springs and struts on a stock stang are separate. You can just put the car on jackstands, then jack the control arm up a little and leave the jack holding the arm up while you remove the old strut and install the new one.

Tip...remember to mark around the two bolts/strut assembly that hold the spindle/brake assembly. Replace the new strut to same position, this will retain original camber/caster to some degree.