I have converted a much more pedestrian, but still roll film old Polaroid J66 to use rolls of bulk loaded 70mm long roll portra 160NC c-41.
The modification was to drill a hole for one stove bolt to pop out the 'top' to serve as a means to wind the take up roll. Take up roll is a 35mm spool with a bit of whittled dowel spliced in the middle. Feed spool is just plian dowel. Black gaffers tape and cinefoil has been used to close off the area where the backing paper once exitted.
With the 70mm film the aspect ratio is closer to 6x9, but on steroids. It must be loaded and unloaded in the darkroom.
I limit my roll length to that equal to 220 film, so as to be able to use a modified paterson reel to develop it in a roll film dayllight tank.