This episode stars Dennis Weaver (older Lacy Fletcher) with all three of his sons--two acting and one producing. Robert Weaver (George Lee Jessup), Rusty Weaver (young Lacy Fletcher), and Rick Weaver (coordinating producer).
The "Nashville number system" referred to in the story is simply a way of writing music by giving whole notes a number from one to seven and is most commonly used for chord changes. For example, a traditional blues song would have a progression of 1-4-5, such as a C chord, and F chord, and a G chord, with the C representing 1, the F representing three whole notes higher (4) and the G being one step higher than the F, or (5).
This episode features two Star Trek alumni. Susan Oliver was in the original pilot of Star Trek (1966) as the intended love interest of Captain Pike. The singer at the country/western bar was played by Amanda McBroom, who played the JAG Captain in The Measure of a Man (1989). McBroom is not only a singer in real-life but a successful songwriter as well, with her compositions being sung by a who's-who of prominent entertainers of the seventies through nineties.
When Fletcher and Magnum are in the archive looking for old phone numbers, Magnum mentions Ms Jones at the Records Office. This is the person Magnum had problems with in two previous episodes. In the very next episode Ms Jones would become his client.
String quartets don't require conductors. They play off the movements and direction of the first violinist.