Hi, I'm thinking about getting a A16 back for my SWC/M. My model has the later plastic viewfinder. I can't seem to find a mask that would help composing 645 in the viewfinder. The Hasselblad mask that's rather easy and expensive to find fits the first version the viewfinder. Also, I assume there is a proper mask I can use with the focusing screen adapter and Rmfx Viewfinder? Want to be sure before spending more money...again. Thanks.