Yeah, I'm in agreement with the other posters on this topic. The RB is a great camera just as it is, and I wouldn't start messing with it. If I really wanted 6x6, I'd get a mask for the viewfinder that crops down the viewsreen to a square and crop off the rest under the enlarger. Hand the extra two frames you get with a true 6x6 camera. You'll need to run many many rolls of film before you recoup the cost of a 6x6 back. And besides, with a 6x6 back, you loose the option of making a rectangular negative and its extra real estate.