Lee, That's the kind of thing that can drive you crazy. I'm glad you found it. I'm sure that your truck has factory turn signals because Lt Blue Left, Dk Blue right, Brn Parking lights is the same color coding as my 1971 and a 1977 I was working on today for a friend. I am pretty sure 1958 is when signals became standard because I have seen 1957s that had to have them added. I'm sure Bill knows and can tell you. No value to knowing, just interesting side information.
best wishes,
Les
