I can't read the number under the M5, but it looks like a 9. These would be correct for 1970 B- and E-body by date, and also found on 1971 models. These are hard to find, especially in this condition. The last set I had was from a 1970 RR, and as nice as yours, but factory purple and all four dated within a few days of each other. I got $750 for the four of them, and that was several years ago.