Big brake upgrade for a 1971 dart with original KH front discs

The Cobe-style 13" Front Disc Brake kit looks interesting, guess I would need to replace the spindle to a 73+ one, or hare there a bearing kit/shims/sleeves available to use the 73+ disks on an earlier spindle?
Am I correct that it uses Ford Mustang Cobra dsics and callipers? Anyone know form which year those come from?