Early TJs had the clamp over the top. I think later ones changed to a clamp at the base.
If you look at the pic, there is a bent plate at the rear which holds that side of the battery. The near side looks to have a hole in the center which should be threaded. A plate would bolt down there to secure the battery.
The same seller on ebay has the clamps which look to be a plastic block. I've made plates that do the same job though out of angle iron in the past. This pic I've just made in MS Paint should give you a rough idea.