I've taken measurements from my Mamiya Super.
The film plane/shutter opening is 58mm wide by 43mm high.
The lens opening cavity has a baffle that I had forgotten about. It is irregular in shape, but at a minimum it is 44mm wide by 40mm high.
The depth between the front of the shutter curtain and the front of the camera/lens opening/front baffle is hard to measure, but it is a minimum of 54mm (to the baffle) and a maximum of 64mm (to the varios bumps on the front of the camera.
At most, there is 2mm from the front of the shutter curtain to the back of the camera body.