On shooting Polaroid/Fuji Instant Film on 2x3 (6x9cm) cameras your statement is incorrect.
Originally Posted by rawhead
There was a Polaroid back made for the Horseman VH/VHR that can be used on other 6x9 cameras if they have a Graflok back. I used one on a Horseman VHR and later used the same back on a Gowland 6x9 view camera. I'm sure that it won't fit all 6x9 cameras, but will fit a lot of them.
If you buy one it's important to get the ground glass spacer with it. There was also a rangefinder spacer included with it so you could use the VHR hand-held but this would probably be a moot point on anything else.