AC:
No they mount on the bottom. The rear mount is a plate that goes right on the bottom of the existing u bolts. You just place the plate on the bottom of the u bolt and use the supplied nuts. It only takes about 5 minutes to install the rear mounts. Then you attach the bar and the front mount. Place it up to the frame, mark and drill the front hole. Remove the bar from the front mount, slip in the frame strengthening plate (which has the nuts welded to it)install the front bolt and then mark and drill the second hole. Attach the bars again and adjust the bars(simply by turning them by hand) and tighten the jamb nuts, thats all there is to it. Lsfarms instructions were right on and made the install easy.
On the rear mounts you need to have at least an inch of excess thread on the stock bolts below the existing nuts which stay on, or you need to get longer ones (so that there is room for the mount and the additional nuts). I had more than enough excess threads on my stock bolts. I dont see why they wouldnt work on a 3500.