The lock ring on Ebay http://www.ebay.com/itm/142015687206?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT these were available from dealers until fairly recently.

The large gaps in the lock ring are similar to the 73 Charger one I have. I'll post a picture of it and the gas tank section it locks into. Theres a new feature in the newer gas tanks (73 and up?) that wont allow you to use the older lock rings.