Well. Many years ago, I was building a 70 Challenger stocker. Long story but I never ended up finishing the car. I was advised to change it to a 71 as well. The grill is no big deal. Just swap it and the latch tray. You have to modify the rear taillight panel pretty severely. Remove a couple of the dividers and patch the one in the middle where the 70 back up light is. The bottom outside corners need to be cut bigger and you drill lots of holes for the panel that surrounds the lights. Send me your email and I'll shoot you some pictures of my panel that is modified. Of coarse by not racing it as a 71 stocker, I wish I had never hacked it up. I bought a tube frame car and raced it at my local track