I'm in the process of restoring a 71RR and compared to the 70 Challenger I finished 3 years ago, they are much more difficult to restore. Just like it was mentioned already low production numbers and only 2 yrs in production. Now on the good side, AMD now has some sheetmetal just out earlier this year. I just picked up a set of quarters for my project and they do look nice. If this is your first restoration buy the best project you can find and do your homework.
Lastly, they are very cars when done, well worth the effort. Good luck