I don't have any pic with a close-up but if you go here you can see how it works. Makes putting the tent on a breeze. Quick Release Tent Mount Kit - by Front Runner
I don't think the limiting factor would be the rails but the roof capacity/load distribution. Meaning even if an aftermarket rack could hold 10x as much it doesn't matter as the factory rails with these crossmembers can far exceed capacity. The limit may even be a center of gravity/safety issue.
I used 1/4" hardware with my FrontRunner accessories (just bought RTT quick mount) and after putting 1,800 miles on it with the 1.6m Stargazer I feel confident it is the answer for me.
I assume the M8 wont fit in the 1020 slot right? Maybe the 1530 or 4590 profile would be better? How rigid is that 1020 on that span? I have a Slimline II but would rather just do this for as much as I use it. Going to put my tent up there. So the same 1/4" hardware you used for the 80/20...