The '72 and earlier have two piece rotors (the hub is removeable) whereas the '73-up style like yours are one piece. The inner wheel bearing is a different diameter so you can't swap rotors between the two without doing some sort of conversion. I understand that they make a special inner bearing that allows you to use the later rotors on the earlier spindles. The '70-2 disc brakes also used the pin/grommet caliper mounting instead of the sliding caliper like yours. I can't tell which spindles you have from your photos, however, so no telling what they were originally on without some forging numbers.
