Correct R, L, 058 that's why I said date code, and it is a 68 cuda so it fits, measure them and you will see if they are 340 .087" or 383 .089", you are probably right blue paint 340
On board, just looked at some notes I kept as I did not take pics at resto but the other end of the bars had 098 With an L and R on them. My build date was a 10/68.