Fixed Up North

I haven't gotten any responces in the mechanics forum yet, so I am going to post my question here too. I put some Empella Frogglegs on yesterday. I got the front brakes on without too much difficulty, and the rear cantilevers and cables went on fine too. There isn't enough room between the rear cantilevers and my rim forthe brake pads. I tried a Koolstop pad that I had from my old setup, and it was also too big. Anyone else run into this? Do they make low profile brake pads or can I modify my pads by cutting away the part that is interfering? Is it possible that my frame is too tight to run these brakes? Thanks for any help.