I've dismantled/restored several Chevelles myself, and one 69 El Camino and none of the Chevelles had the cushions on the cross member. The El Camino did have the cross member mounts. They were used to support a load that could be put in the back of the ElCamino/Wagons. I guess it's possible that some Chevelles got them as they were heading down the line, but they weren't suppose to according to the factory assembly manual.
Here's a scan of the body mount page showing the rear cross member mounts as Wagon & Pick-up (ElCamino) only.
