Interesting note on the Chuck Conners apperance on the Adventures of Superman series...I saw that episode again in the 80s on WGN-TV...and yes he was mentioned in the closing credits. And according to Wikipedia, it was Herschel Burke Gilbert who directed the orchestras that played the Superman March theme and later for The Rifleman theme.
Gilbert in his day was a rather prolific musician...He played in the string section of the Harry James Band. He did countless TV themes including The Big Valley,Gilligan's Island,Gunsmoke among countless others.
Back in the 1950s and 60s it was the theme that sold the series..something that even carried over into the 70s....and Gilbert was in demand of his services. What made The Rifleman theme stand out so much was that it was a full orchestra with plenty of reverb to give it a bigger than life sound...which was common practice from record producers in that era which included the likes of Mitch Miller for the CBS labels and even Phil Spector's Philles Records.
You need the music to sell the show, examples....
The Lone Ranger (William Tell Overture)
Charlie's Angels
Hawaii Five-O
Happy Days
Touched By An Angel
...and I can go on.