It uses two of the factory holes. You can also drill 2 holes on the ends, but most of us haven't. The 2 factory holes and the 3M tape is more than enough. It does, however, cover the 2 remaining holes. Though, you'll want to use some silicone or something to keep it sealed.
This may be a pretty stupid question, and maybe it will all make sense when I receive my GT500 spoiler on Friday, but do you just squirt some silicone around these remaining holes?
I put a Shelby spoiler on my '08 V6 and it fit perfectly. The shop that installed it said it was quite simple and it holds like a dream. But then again, my Mustang came without any spoiler so the holes were drilled.
I bought and installed the OEM spoiler before everyone had them a/m and prepainted, it uses all four factory holes, but with the 3m tape they have on the spoiler it would have held without any screws, so I'm sure 2 screws are plenty.
Thanks everyone for your replies! I got mine on this weekend, and it looks great!
I was really worried about getting it on there crooked tho, so came up with a plan that really helped me:
When putting the 3M tape onto the spoiler, I used an additional 5 inches or so, on each side. I then removed the sticky part of the extra tape but left the red plastic that covered the tape. I could then put the spoiler onto the car, without having to worry that it would stick. I got it where I wanted, gently attached the screws, and then used the red plastic that had covered the extra tape, to just pull it off the rest of the tape.
I got my GT500 replica spoiler from Atlanta Mustang. It also only uses 2 rear bolts, the fronts aren't used so I just used some silicone sealant to seal them off. The tape along with the bolts is more than enough.
The GT500 spoiler is by far my favorite spoiler for the S197. I plan to get on for my GT this spring.