Tony, the early and late style rotors are not interchangeable unlesss you change almost everything (rotors, struts, calipers and the wheels, pads and possibly even the lug nuts.)
a) rotor/caliper/strut. The offset built into the design of the strut, caliper and rotor are different by roughly 1/8 inch.
The late style rotor has a hub centric flange cast into the area surrounding the outer bearing. This hub mates up to a machined hub centric hole in the late style mag wheels which assures the wheels are centered on the hubs. This is a very nice upgrade to your early car if you do it right, namely replace almost everything. You may even have to replace the lug nuts to make sure you are using a set that is right for your late style (mag) wheels. The mag wheels use a longer bolt.
c) I'm not certain of this item but it seems to me the later cars used thicker brake pads. Maybe someone else can chime in on this item.
d) The early style struts used a thru bolt to clamp the lower ball joint to the strut as well as a ball joint intended for use with a thru bolt. The later cars used a tapered pin arrangement that also used its own style of ball joint. Intermixing parts between early and late cars would be VERY dangerous.
I'm not trying to talk you out of this conversion but be sure to do it right. It is much more then just a rotor change.
Early would be the 70 thru 72 model years. Late would be 73 and up.