BULLSHEET. The camera has a B setting. The shutter release is threaded for a cable release. If the shutter will not operate with the back open then look in the edges of the camera back for levers/pins that are depressed when the back is closed, lock them depressed with wooden pins such as round toothpicks. With the shutter locked open on B with a locking cable release the film plane to lens element can be measured. With the camera mounted on a tripod, lens critically focused via the viewfinder, shutter locked open on B a temporary ground glass held at the film plane should match the focus at the viewfinder. A temporary ground glass can be made from a piece of glass/or clear acrylic cut to fit the film plane with strips of clear transparent tape placed next to each other without overlapping, the tape side goes toward the lens. With the shutter open on B a block, be it your finger or other blunt object can be placed in the shutter curtain track to block the second curtain from closing when the cable lock/shutter is released. The curtain may be movable from full closed with the shutter released, use care not to damage it by poking holes in the curtain or bending the light trap edge. The problem is the redesign of the lens, figuring out how to compensate for it will take some careful measurements, investigation, and testing to figure out. A modification to the lens or body will likely make the lens usable on that body only, that body only usable with that lens. A modification that cam be added or removed easily to either the lens or body is the idea solution. There is no Do This fix.