It only applies to a certain few. When you look at a set of rims there are 4 things you need to keep in mind.
1) the overall height of the rim, In this case your looking at 18".
2) the width of the rim, in this case you are looking at 9"
3) the bolt pattern. the rim needs to be made to fit your axle.
4) the offset/backspacing. Sometimes referred to as ET. This is used to determine how far off the axle the rim is going to sit.
1 and 2 need to mach up to the tires, and 3 and 4 need to match up the the car (and you need to take the tires into consideration. 3 is no problem the 04 and 05 mustangs use the same bolt pattern but in your case its 4 thats going run you the most risk of not working.
The stock rims/tires on our v6 cars is usually 16x7et39 with 215/65-16 tires. The 94-04 saleen had 18x9et24 rims with 265/35-18 tires (based on what I could find on ebay)
so if we go to
my favote tire website and plug in that info we get this...
Keep in mind, the mounting pad is going to be in the same spot, so your car would sit lower to the ground, there will be more open space above the tire in the wheel well and everything is going to stick out a bit farhter (so there could be rubbing while turning)