I have a very compact 9x12cm SLR which I believe is a Klappreflex-Kunstler-Camera. The model number 755 is stamped into the leather handle. When I obtained the camera, what appeared to be an empty bulk film magazine, marked 742/6 was inserted into the camera back. I'm not at all familiar with these large format SLRs but would there have been a ground glass back for alternative composition and focusing? I have a number of different 9x12 holders but none are compatible with this camera. Is 742/6 the model number of holder that I need? Are there any other holders from different makers that will also fit?