I'm putting together a Hasselblad SWC-alternative camera using a Mamiya RB67 revolving back and screen and a Rodenstock 35mm lens. I'm a Hasselblad user, but Mamiya backs go for a fraction of the cost of Hassy backs and with the latest revolving backs you can make use of 6x4.5-6x8 film holders. I'm not familiar with the RB67, though, and I would like to know whether it is possible to use a chimney finder or a prism on the back of the camera (as you can with the Hasselblad SWC) rather than in the waist level position. The camera will have an external viewfinder on top, but since it will also have some shift capabilities I'm looking for some way of efficiently viewing the back screen for more accurate framing. Thanks in advance for any help.