I would do as KitCarlson said and get you some graphite to put in the ignition where the key goes. You can get some graphite at home depot. I had the same thing happen to me. The key didn't break,but it would not go in. After I sprayed some graphite in the lock,it loosened up and the key works...
I found this 74' duster on craigslist. It was so reasonably priced,I couldn't pass it up.The 73-74 duster is my all time favorite car.It has the /6. Yes I would rather have a 340 but I'm happy with it for now.