(Right hand raised) I have bent….or cold set…that sounds better….Mafac calipers before. I feel better about the manipulated washer approach just because. I completely agree that Mafac calipers are tough.

Those Amazon bushings linked above are actually bearings on the OD, not the ID. Not sure how that's useful for anything. Probably much easier to make than the bearing that we want for Mafacs.

I have bent many hundreds of Mafac calipers without incident. It's difficult to bend them enough, and it's a bit awkward to put a wrench on there to bend them.

More commonly they need adjustment of the upper arms, so they do not come into contact as they are raised.
That's pretty easy (with the arm removed) - hold it horizontally in the vice with a pair of soft jaws and the pivot hole extending out to the side, inset a suitable bar in the hole, and twist.

This might not apply but I had to add toe-in to vintage side-pulls with fresh pads, and added a half-washer to the stack. Possible application here would be behind the front washer of the 456E assembly. I cut the washer in half using a big pair of side cutters. A brass washer would assure nothing else gets nicked up.

Mine was a "temporary" fix while I looked for something better, but has proven up to the task and I'm leaving well enough alone.