@moab cj5 so these measurements are a little rough but maybe they will help. If you haven't, I'd contact White Knuckle to see what if they have sold any to GX owners.
Sliders are 68" long. That is the pointed tip of square tube end to end.
The u bolts are 7" center bolt to center bolt
The 4Runner frame is 6 to 6.25" tall. 6.25 at the rear, closer to 6 in the middle, and 6.125" tall at the front slider mount.
The front pointed front end of the sliders are 4" from the wheel well measured at the start of the body seam.
Body mounts between the GX and 4Runner may be different but from the body mount weld to the center of the front u bolt (lower end of u bolt) is 4.125". I measured from the back edge of the body mount weld to the u bolt.
The u bolt center to center distance from front to middle mount is 23.625".
The u bolt center to center distance from the middle to the rear mount is 22.25"
From the front edge of the LCA mount weld to the center of the rear u bolt (lower end of u bolt) it is 2.75".
The top of the slider main square tubing is 3.75" below the frame.
The tubing sits 1" below the 4Runner body seam.
Both sides measured up roughly the same but as mentioned in the original post, there are brake lines on the driver side to work around. See if the pictures help and see if your brake lines are run the same way. They run along the inside of the frame before middle mount and then curve up to get between the gas tank and frame. At the end of the gas tank, they turn and run up on top of the frame.
Let me know if there is anything else I can help with!
