I was having a read of this thread: (there was a url link here which no longer exists)
and saw that the backs are not interchangeable. However, can you detach the revolving adapter from a rz67 and mount it on a rb67 pro S to work with the rb67 back?
My RB67 is missing the adapter and I am finding it difficult to find one locally.
On facebook there is a group called Film Photo Gear, you can search for it but I think you need to request approval to join. Anyways, there's a guy on there selling an rb67 revolving back (pretty sure that's what it is) for cheap.
If you do not find what you need I would contact KEH. I'm sure they have cannibalized units and pieces that can be bought as such. I could be wrong but as much used RB gear as they've had over the years I would assume they've got stuff like that.
Keh looks good except shipping is prohibitive to Australia.
It looks like there are some floating around ebay which I can get for $80-100 USD shipped. There is some guy in HK selling these parts new.
I will check out the local film photography groups and see whether I can find one. I don't really want to spend too much on it as I am not sure whether the stuff I have works or not.