I did this to get the FD on my Schwinn SS. As I remember, I used a metal file that was rounded to just under the profile needed for the FD. It took quite a while, and was a bit tense knowing the FD was likely going to be unusable if I managed to mess it up. Filing at the ends of the clamps is where most of the material was removed to allow it to go over the wider tubing. In the middle I did remove some, but the clamp itself can bend a bit to get the new radius. Wound up using the same bolt on the clamp as on the other bike. Left a bit more of a gap when clamped than on the old frame, but works just the same.