I believe Kutter is right to consider thinning the entire spring, if that's what it needs. Thinning just the bend, i don't think will hurt it as a spring, but may put all the action of the spring at the bend and not distribute the forces along the leafs.
It may be slow going, but I think you can thin the spring by working it on a flat plate with oiled wet and dry sheet abrasives. If it functions as a spring, the temper of the steel will be plenty workable. If you thin it with a power tool, I'd try to hold it by hand to stop if you feel heat, but that's probably not so easy to do. Don't lean towards the ends of the leafs, they may cut quicker than the bend, and consider breaking any sharp corners that might form.
If these springs are hard to come by, maybe you could trace out both of them and measure an bunch of different points on them to save as a reference. Best of luck with it.
