Check if your HJ has had panel work on the rhs, that cap is the HX/HZ/WB style. The HQ/HJ filler neck on the utes/vans have the earlier style large opening. The vented type has smaller diameter opening with smaller width locating lugs. My HZ sedan had the same arrangement but the cap was of the zinc plated pressed type, now that was a pain trying to get it on and off through the back bumper. Sitting in my back yard at the moment are 2xHX,1xHZ,1xHQ, utes and 1xHQ wagon. The HQ and 9/76 HX have the same type early cap, the 6/77HX and the HZ have the smaller diameter late style cap, and the HQ wagon has an early style fitting locking cap. The different fitting caps on the HXs are the reason I posted the question about the change of caps and filler necks, a couple of weeks ago. I have also got an original HZ panel van cap and an HR cap floating around somewhere, over the Christmas break I will take photos of all of them and post them up.