You’ll like the MSD 2-step. I put one in my 2013 GT. I can look through my old photos and send some pics of the install if you like. Just let me know. Here is a quick post on how I wired mine up. I can’t see it being any different on the S550. Very simple install. The most difficult part of the install is routing everything nicely and neatly, which I know you would definitely want to do, based on what I can see of your build thus far.For sure. I’ll post it and video it. Probably won’t go on the car until June sometime when I have a break in racing.