The brake pedal on my Coronet has very little modulation. The pedal seems a little low, but all I have to do is breathe on it and it locks the fronts. I swapped to A body slider calipers and replaced the booster with a NAPA replacement that looks like the Midland Ross with the clamp around it. MC is either 1" or 1 1/8. As soon as I touch the brake pedal it almost feels like it gets sucked down. Could the booster be bad or wrong size?

coould the master cylinder be the wrong size? Smaller piston means more travel and more mechanical advantage and easier movement. LArger means less travel and less advantage. IF the booster is "sucking" your pedal down (it is designed to assist, not take over) maybe you need a larger piston in the MC or less assist in the booster? Just run a bigger cam (just kidding);-)

Might be (if I recall correctly) a reaction disc missing in the booster.