Going back to '71, good luck.
Last I used carfax a few years ago, they didn't go back furthur than '78 or '79.
The info get's less and less as you go back. I doubt you'll find any way to tell if your '71 was ever in an accident. Just look it over real good, there are usally tell-tale signs, a little overspray from a re-paint of a section, and mask mark in the door jamb, they are there. Of course, your '71 may have been re-painted, 2 or 3 times already just out of age.