The issue you are running in to is one I discovered after many bombing runs. Not keeping your wings level is not near as important as not maintaining 1 positive G. I believe this is a built in safety feature which makes sense when you think about it. If you are pushing forward on the stick even just a little bit, the bomb could possibly hit the bottom of your airplane when it's released. Even with the power pulled back and speed brakes out, the airplane will still accelerate in a dive which creates more lift causing the nose to rise. Before you roll in, put in a fair amount of nose down trim and this should take care of the nose coming up. I love the Sabre and fly it almost every day, just don't ask me to explain the mcb bombing system, I still haven't got that one figured out.