Please do yourselves a favor. If you can only have one, keep the 71.
After a few years the new Challenger you buy with the 12,000 from the 71 (plus another 30,000 or so) will be just another used car worth about 12 grand. I have had old Corvettes and new Corvettes, Old GTOs and New GTOs, Old Camaros and new Camaros. It is always the same. Five years later the old one is worth more than ever, and still draws a crowd. The new one is just a used car worth a third of what you paid for it, and nobody gives it a second glance.