I hand slice 70mm to reload onto 120 spools/620 spools and the width is not always precise enough for stainless reels.
I use large rubber bands (about 1/4" wide unstreched) that the evening paper comes held together in to adapt the paterson roll to the narrower film.
Put the bands a few loops deep on the narrow portion of the shaft, until they fit snugly and then don't try to get the larger half to twist back into the usual 120 spot notch; just roll some of the rubber band over the wider diameter shaft, and all will hold in place. The ratchets are not excatly across from each other, so things are a bit trickier to load, but the method works.
If I do this more often I was thinking of cutting the shaft tabs off of one spool's larger diameter, and then space it the right distance apart, and make al fast by winding the joint with self amalgamating ruber tape. It works great for this kind of applcation, where you want to start with something flexible, and end up with a mass that is a solid.