I am about to do the same with GX550 sliders on my ORP. Just going to do 8mm rivnuts since I already had a bunch. Mine appears to be 14 total for the 8mm bolts and then 4 for the 10mm bolts that for some reason do have the threads...
https://www.zroverland.com/product-page/lc250-gx550-slider-step
I bought a pair of these to make it easier to use the sliders as a step. I thought about just replacing the sliders with a set that has more of a kick out or flat surface to step on but decided to just save the money for now. They wouldn't be the best if you're doing serious off roading because they attach like scope rings and create a right angled surface on the bottom of the rail where the rings attach that would not do well getting drug over rocks. But for lighter off roading like what I'll be doing, all of my impacts on the rock rails have been on the lower tube, not the top one where this step attaches. They've made a big difference for the ease and comfort getting in and out of the vehicle for me and my girlfriend.