I trimmed the horns, no problem. You have to cut them completely off. I had to do that with another brand of HD bumper on another one of my D1s.
That is a good idea but there is also interference at the bottom of the rear quarter panel. The SG bumper attaches to the body where the factory ”splash” panels mount. It is the panel that the factory mud flap is attached. The SG bumper replaces those parts, it has a built in panel for that. The lower part of the quarter panel prevents it from going high enough to reach those splash panel mounting holes. Moving it rearward enough to help would put it too far back to make those mounting points not work. I don’t think there is a way around some trimming of the lower quarter panel.
I have kind of wedged it on and damaged the lower part of the quarter panel. So, it’s not the end of the world that I have to cut off that area, now.
I searched online for SG install instructions and came up empty.