I know from personal experience that the CS56 does require a spacer to clear the Brembo calipers. I am in the process of fitting mine almost as we speak. The tires are due tomorrow, so I should have them mounted early next week.
Here's the deal for those who care. When I got my CS56 wheels (that the fitment matrix said would fit the GT500) I figured I would test them anyway before going off to the tire guy. They clear the caliper, but not the paint on the caliper. That's it in a nutshell. To make one of my typically long stories short, I bought a set of H&R 5mm (~ 0.190") spacers, stock# 1065705, from Livermore Performance in CA. The instructions of the H&R website (I think that's where I saw this) say you need at least 8 full turns on the lug nut on the 1/2"-20 studs to secure the wheel safely. With the 5mm spacer and the CS56 I got 7-1/4 turns. CRAP. After some more research, the only long studs I could find that had the correct 'knurl diameter' were the ARP 100-7714 Mustang II (don't say it!) front wheel studs which I got from Jegs. I shortened them and turned 1/4" at the end to remove the threads like the stock studs. To determine the correct new stud length, I got a new stock replacement Ford front wheel stud, then placed it against the ARP stud such that the end of the flanged end of the stock stud matched up with the inner edge of the flange of the ARP stud. In other words, the overall length of the ARP stud was longer than the stock stud by the thickness of the ARP stud flange - about 1/4". I did not put a flat on the ARP stud flange the way the stck stud has a flat spot, and it was not necessary - installation had no clearance issues.
I used a drift punch and hammer to drive the stock stud out of the front wheel hub. It takes a few smart whacks, but no sledgehammer blows, please. If you align the stud you want to remove with the center of the caliper (the wheel hub at the 9 o'clock position on the passenger side, the 3 o'clock position on the driver's side) you can push it right out the back without hitting anything. I put WD40 on the hole in the wheel hub, and used an old lug nut to pull the stud into the hub. A word of caution: have several lug nuts handy because you will probably gall the flat end surface after a few studs. (I used the conical end of the lug to seat the stud for the first two turns, then turned the lug nut over so that the flat surface faced the wheel hub / brake rotor for the heavy work of pulling the stud all the way home.) Also, have a large flat washer handy to put under the lug nut so it does not gall or scrape the outer face of the brake rotor hat. Finally, I had to use an air impact wrench to torque the lug nuts sufficiently to pull the stud in. It was too hard to try doing it by hand and holding the rotor from turning at the same time. I would turn the nut 3 - 4 turns, then stop and look behind the hub at the stud flange to ensure it was going in straight and true. Had no problems with any of the ten studs, just work carefully. Doing it this way meant not having to remove the caliper and wheel hub.
When I tested my work again with the spacer in place and the CS56 rims, I was able to get twelve turns on the lug nut until itsecured the wheel. Plenty of margin.
A final word about the length of the ARP studs. I chose the length carefully after measuring the inside of the stock GT500 lug nuts. I verified that the stock wheels - without the spacers - will fit without bottoming the stud on the inside of the cap of the stock lug nuts. So, if for any reason I change wheels or go back to the stock rims, I can take out the spacer and be back to stock again.
HTH
