It do get confusing, The SC of S&W does show a three letter (ANB5318) for a 1986 variation, However, a Model 60 with no engineering or production changes was made between 1965 and 1969. The R prefix started in 1969. So, either you have a late 60 after 1980 and you missed the dash number under the yoke or you have a rare "made before it's time" firearm. Best I can do, anyone else?