'75 Duster B body front brake upgrade impressions wanted

I'd start by seeing which brakes will lock up first.....front or rear. Then get an adjustable proportioning valve and get it to where both ends lock up a the same time. That should shorten your braking distance about as much as you're going to get IMO. Going to bigger brakes will just keep them from wearing out as fast and keeping pedal fade from happening as easily. Going to a tire with a better traction rating can help on your stopping distance too.