Look at a 2000 Crown Vic/Town Car. It has 12" fronts and dual piston calipers. I'm trying to put them on my '64Dog D100. None of it is very expensive and the CV has cop brakes available which if they can stop a cop car weighing at least 5000 lb they should be overkill on your A-body.
Or try the PBR or Viper calipers.
R.