You could run a manual setup with the factory calipers and 11.75 rotors up front. It would stop but you might need to put more effort into it than you're used to. Once you changeover to the 13 inch rotors the effort would drop a bit.

I run manual brakes on my Coronet with 13 inch rotors up front. It stops really well and that car is 4000 lbs. So if you car is less than 4000 lbs you should be fine with manual brakes.