I believe 1970 was the last year for the metal closures. You can see a good shot of one in photo 4 down in the right column of this 70 Caravanner. If I could figure out how to make an aluminum one to put on my 71 - I'd actually prefer that and replace the plastic slide.
Our 71 has the aluminum swinger. I think is it original. If it were here at the house I would snap some photos and post them. It may be a "trim package" or "upgrade " I like the swinger door. It is kind of fool proof for the kids.