I think I have a dumb question - how are you planning to put such a back on a grpahic?
Are you totally giving up on the OEM ground glass? We are talking 4x5 cameras, and 5" is 12.7cm to me, which is a good deal under 17cm.
For my franken-mod panoramic MF camera I converted an old polaroid J-66 roll film polaroid. Auto shutter still works for me. I ND filtered the selenium cell to have it auto expose for the 160 speed film I use and not the 3000 speed it was built to automaticaly adjust shutter speed to expose.
It now sports a darkroom load and unload 5' long spool of 70mm bulk roll film. Low tech - so many tuns of the knob to advance.
I added a winding knob/ extended length 35mm cassette spindle driver at one end of the camera to advance the film.
So far for the 3 hours of mod, and $10 to buy the camera at a thrift store I am happy with the two rolls I have shot using the el-chaepo plastic Polaroid lens in this camera.