You likely bought the wrong version rack. The GX has 2 different roof racks. One for a low profile roof rail and the Overtrail roof rail (that is similar to the LC). The low profile roof rack screws into the low rail and the one you need has the integrated clamps for the raised rail. As far as I know, the attachment points are not available separately.I bought a used GX550 roof rack, but I need the parts to mount it to my LC250 rails. I guess the Lexus owner had it mounted directly to their roof channel. Do you know where I might find the parts to help?