Just yesterday I looked at a cap from a deluxe tank ( i thought) ... not sure what year, but it fit my custom. I did not try and use it as the custom cap has a lip that goes over the outside of the tank filler and the deluxe did not. I thought it might leak on a full fill...
Maybe mine was a standard tank cap on second read of your post as I was not aware of any difference in the locking arm or locking cap. ( I thought they were all the same two piece design and did not have that part)
My smaller canon camera is dead, otherwise I'd post a pic...