Running the 11.75” disks up front with 11x2.5” drums out back works really well. I’ve run that combination on both my Challenger and my Duster, it stops MUCH better than the smaller factory disk/drum set up.
These cars weren’t even designed for radial tires, so the “designed for” argument goes out the window pretty fast when it comes to tires, wheels, brakes and suspension. Adding radials, even narrow ones, significantly changes the grip at the wheels which effects everything else, including the braking.