For the hooks, and the front 2 bolts on the hitch, I used 1/2" x 3" Grade 8. The rear 2 bolts on the hitch, I used 2 of the bolts that came with Kens hooks.
Be warned when you drill... that the weld is centered front to back in the bottom of the tube. I learned the hard way!
My original plan, was to drill/tap the top hole, thread the bolt into it from the bottom up, creating a stud for the hook plate, then drop plate on, and put nut over it. I opted against it, because the nuts were too tall, and would have interfered with the chain and hook.
I know Ken urges against clamping the tube like this, but the LS tubes look pretty thick, and I couldnt see any other way of doing it that I would have been happy with.
Like my buddy says... if the hooks start to get loose, you know you lifted something too heavy!! LOL