I believe Sheldon mentioned he had got the spacer, thanks.
No, the rack is not too heavy for off road. I had a support brought up from the sliders to take the majority of the weight (I had my spare 35" SSR on top). Every once in a while off road if we hit a sharp drop at speed I would hear a "CRACK" from the top though. There were no issues on pavement. I do not see any damage yet from the off road portion. I have decided that the truck will get a cage at some point, and anything I put on top will go on that cage. The rack will be good for someone who wants to place lightish loads on top. If one was to place a thin metal brace in the fiberglass channel where the feet clamp, the load would be distributed better along the whole lip...but even without that it will do awesome for someone who wants a rack for the top of their BJ74. The system I used used the channel at the back, and the channel above each door. No drilling of the top required. I have not totalled my costs yet, however it will be sold at a discount.
It was different driving with weight up top...that is for sure.
gb