What size tires, and MAKE tires do you have on the car now?
Do you know the rim width? Take a pic, they are likely a standard rim.
Now, get on a flat and level surface,
check the air pressure air all of the tires, and
Measure and report ALL four fender heights.
Then, we can go from there.
Do you want better handling? A little lower (my suggestion)? Best ride comfort with handling (stock GT). Best ride comfort period (4 cyl springs)
My sugggestion is to go with Mach1 or Bullitt springs since they are the ONLY SPRINGS SPECIFICALLY FOR A MUSTANG! (not counting the very stiff Cobra 95 R springs).
Otherwise, you're likely getting some hack ***** job by an aftermarket company that just want to sell CR*P! The exception is MM (Max Motorsports). But, IMHO, their springs are NOT designed for otherwise stock mustangs (FCA ,
LCA, stock rear
suspension, etc).
It is possible to go with stiffer springs (like the Mach1) and still have close to stock fender height (~~27.25 to 27.5").