There are only about 3 basic Chevelle style rotors. The 72 and earlier, the 73/78 and the 79 and up rear wheel drive.
That pretty well limits the choices when you carry one into the parts house and set it on the counter and say "I need two like this".
There are some distinct differences in the rotors.
The 72 style has a very short hub sticking out as compared to the later units.
Do the spindles have removable steering arms or are the steering arms cast into the spindles? 72 and earlier had bolt on arms, 73 and later had the arms cast into the spindles.
you can compare the photo to your rotor. If that doesn't match put in 1975 chevelle Or Malabu
By comparing the photos you should have a better idea of what you have. Then you can bop on down to the parts house. Armed with a print out of the page to help get a better price.
the main link is www.partsamerica.com