What Year Did Cover Change?

The olddman has a question! I have a 1965 Dart GT with the Charger 273 engine. Last year I had to replace the timing chain cover and discovered that you have to remove the timing chain cover in order to replace the front seal. After replacing the cover, I read somewhere that the timing chain cover was changed a few years later so the seal could be replaced without having to remove the cover. Could someone refresh my memory as to when this happened?
Do not plan on having to replace the seal for a while, just wondering!!