The hole has an internally threaded cylinder welded to the back of the dash. So to secure the dash to either the cowl or fire wall, a screw would have to come from the front of the dash some where. I was thinking some kind of bracket secured to the back of the dash that itself would then be secured to the fire wall. I can't find anything close to being able to do that. The distance from the fire wall to the weld on nut would require an 8"-10" screw through the fire wall. That wouldn't offer much strength. The fact that there is a hole in the dash implies any screw would come through from the front. So I'm back to speculating on what would that secure in the 60s-70s? Not a cell phone holder. A cup holder would block the heater controls. I do remember many vehicles with bubble type compasses attached to the dash.