Holiday.
How big was the clamp you were using? I recently removed cotters from two 1974 FUJI 10 speeds that had spent a fair time in the weather. Years of rust on the cranks and the cotters. I thought they were permabonded together. A little WD-40 and a BIG C clamp did the trick. They popped! Really, they popped with a loud CRACK! and fell out of the socket I was using to catch them.

P.S. Trade you that brake lever for your frame.