From my research, it appears there's two styles of main hoop available. One that welds directly on top of the OEM frame rails and another where you need to fabricate a platform to weld inside the rails for it to sit on, you might want to confirm which style the S&W kit has.....
It seems to me that they bent the hoop in a little bit so your harness bar will adjust the width of the hoop if its higher or lower. The lower on the hoop it is. The wider the hoop will be where it mounts to the frame. Vise versa for higher and its narrower. But you just trim the harness bar to fit as needed. And it welds directly to top frame rails