1950 3100 with 1951 rear end

While changing my metal jacketed park brake cables with plastic jacket type I attempted to open the clamp a bit so the larger cable would fit and promptly broke the clamp. Then I moved on to the other side and carefully tried again with the same results. I can weld the clamps back but that is not going to make the cables fit.
Any of you had this issue or am a lone bone head?

Jackie