Alright, Thanks FB, I bought the Shimano clamp-on with that in mind, but had not thought of doing filing to get a good fit. That's a good idea and I guess my question should be if anyone knows what type of clamp-on bosses are the right ones that will accept the retrofit cable guides and which cable guides. If no one knows specifics, I think that filing and making the minor adjustment to make one fit as you suggest should work fine.