The reason the other kits like Border and Tomei have the brackets is to get the angle right. What happens when you go direct to the HICAS mounting points is it puts the arms at an angle and as the suspension moves so does the angle of the tires because the rod pushes the wheel out. I did exactly what you are taking about my car as a prototype and the rear end felt like it was floating after every bump I hit. Not fun at all :-(.
