I remember seeing this when it first aired. Johnny Hart's legendary comic strip, B. C., was brought to life just this one time, in 1973. Once you get past the opening segment where B. C. himself is doing a Jack Benny routine, you'll find this is very entertaining. Cargoplex uploaded this clip to YouTube:
Most folks these days associate B. C. more with a golf tournament that bears his name (it also stands for Broome County, where you'll find the city of Endicott, which hosted said golf tournament for years), than this little-seen special, which hasn't seen the light of day in years.