I have 2 Model 66's. They are both Model 66's with a 4" barrel. One is identified as a 66-1. The other I know was purchased in 1975 by paperwork and is only stamped as a 66. The latter has been modified with a wide knurled hammer spur and a wide trigger shoe. This is the "66." I believe the 66-1 was purchased in the 90's. Is there a difference between a 66, and a 66-1? Also, the rear sight on the 66-1 is blued and the rear sight on the "66" is silver. Any insight would be appreciated.