Has anyone modified a Graflex RH-50 70mm film back from 56x72mm to a panorama format? Does it hold the film flat without the thin metal pressure rollers on the inside of the backplate? Do you just file the window to 112mm or even, as I seem to recall reading somewhere, to 125mm? Is it possible to also widen the height, to use the maximum usable area of perforated 70mm film?