I've been watching this on ENCORE WESTERNS and I see that in some of Dennis Weavers final episodes, both Chester and Festus were in them. Why was this done?

As I understand it, Festus was a well-liked character who made several guest appearances. Dennis Weaver, however, got tired of playing Chester and quit (on good terms) and Festus replaced him as a full-time character.

There were a few early 1960's Ken Curtis episodes where he plays different characters and Ken is so cleaned up and has no twang at all. He also looks so much taller too. According to age records he was 10 so years older than Jim.